<PAGE>

                                                                   EXHIBIT 10.23

                                   GUARANTY

     THIS GUARANTY ("Guaranty") is made and entered into as of February 1, 1999
by Grill Concepts, Inc., a Delaware corporation ("GCI") and Grill Concepts,
Inc., a California corporation ("GCICA") (each a "Guarantor" and collectively,
"Guarantors").

                                   RECITALS

     A. GCI and The Michigan Avenue Group, a general partnership ("MAG") have
formed and are the members of Chicago-The Grill on the Alley, LLC, an Illinois
limited liability company ("LLC") and have entered into an Operating Agreement
governing the operations of the LLC (the "Operating Agreement").

     B. LLC has executed and delivered to MAG a Senior Convertible Promissory
Note in the principal amount of $1,699,000 (the "Note").

     C. In order to induce MAG to enter into the Operating Agreement, to make
its Initial Capital Contribution thereunder and to make the MAG Loan evidenced
by the Note, Guarantors are required to execute and deliver this Guaranty.

     NOW, THEREFORE, in consideration of the above Recitals, which are
incorporated into the Agreement below by reference as if fully set forth
therein; and in consideration of MAG executing and delivering the Operating
Agreement, making its Initial Capital Contribution thereunder, and making the
MAG Loan; and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged by Guarantors, each Guarantor
agrees with MAG as follows:

                                   AGREEMENT

                                   ARTICLE I

                        REPRESENTATIONS AND WARRANTIES

     Each Guarantor makes the following representations and warranties to and in
favor of MAG which shall be continuing representations and warranties so long as
any Guarantied Obligations (as defined below) shall remain unpaid and
unsatisfied:

     Section 1.1. Existence and Rights. GCI is a corporation duly formed and
validly existing under the laws of Delaware. GCICA is a corporation duly formed
and validly existing under the laws of California. Each Guarantor has the
corporate power and authority, rights and franchises to own property and to
carry on its business as now carried on and is duly qualified and in good
standing in each jurisdiction which the property owned by it or the business
conducted by it makes such qualification necessary, and each Guarantor has the
power and adequate authority to make and carry out this Guaranty.
<PAGE>

     Section 1.2. Guaranty Authorized and Binding. The execution, delivery and
performance of this Guaranty are duly authorized and this Guaranty is a valid
and legally binding obligation of each Guarantor enforceable in accordance with
its terms, except as may be limited by applicable bankruptcy, insolvency,
reorganization, moratorium or similar laws affecting creditors' rights generally
and subject to general principles of equity.

     Section 1.3. No Conflict. The execution and delivery of this Guaranty are
not, and the performance of this Guaranty will not be, in contravention of, or
in conflict with, any agreement, indenture or undertaking to which either
Guarantor is a party or by which it or any of their property is or may be bound
or affected; do not, and will not, require the consent or approval of any
governmental authority; are not, and will not be, in contravention of, or in
conflict with, any applicable law binding on either Guarantor or any term or
provision of either Guarantor's charter or bylaws; and do not, and will not,
cause any security interest, lien or other encumbrance to be created or imposed
upon any of such assets or property.

                                  ARTICLE II
                                   GUARANTY

     Section 2.1. Guaranty. Guarantors jointly and severally hereby
unconditionally and irrevocably guaranty to MAG the prompt payment (on demand in
lawful money of the United States) and performance of any and all Guarantied
Obligations (as defined below). The term "Guarantied Obligations" as used herein
means all obligations of  LLC (i) under the Operating Agreement to pay the
Initial Capital Contributions and the Converted Capital Contributions of MAG
(but not the Preferred Return thereon) in accordance with the Scheduled
Repayments, and (ii) under the Note to pay and perform all obligations set forth
therein, subject to the terms and conditions set forth therein (as such
agreements may be amended or waived by LLC and MAG from time to time).

     Section 2.2. Continuing Guaranty. This is a continuing guaranty of the
Guarantied Obligations and shall remain in full force and effect until payment
and performance in full of the Guarantied Obligations. Each Guarantor
understands and agrees that this Guaranty shall be construed as an irrevocable
and continuing guaranty of payment and performance. Each Guarantor authorizes
LLC and MAG without notice or demand and without affecting each Guarantor's
liability hereunder, from time to time, to make any change to the terms of the
Operating Agreement, the Note or in any other term of all or any of the
Guarantied Obligations, or any other amendment or waiver of or any consent to
departure from the Operating Agreement, the Note or any of the documents
executed in connection therewith.

     Section 2.3. Nature of Guaranty. A separate action or separate actions
under this Guaranty may be brought and prosecuted against either Guarantor or
both Guarantors whether or not any action is brought or prosecuted against LLC,
against the other Guarantor or against any other person or whether LLC or any
other person is joined in any such action or actions. Any circumstance which
operates to toll any statute of limitations applicable to LLC shall also operate
to toll the statute of limitations applicable to both Guarantors.

                                       2
<PAGE>

     Section 2.4. Waivers. Each Guarantor hereby waives the right to require MAG
to proceed against LLC or any other person liable on the Guarantied Obligations
or to pursue any other remedy in MAG's power whatsoever, and each Guarantor
waives the right to have the proceeds of property of LLC or any other person
liable on the Guarantied Obligations first applied to the discharge of the
Guarantied Obligations. When making any demand on either Guarantor hereunder
against the Guarantied Obligations, MAG may, but shall be under no obligation
to, make a similar demand on LLC or on the other Guarantor, and any failure by
MAG to make any such demand or to collect any payments from LLC shall not
relieve either Guarantor of its obligations or liabilities hereunder. MAG may,
at its election, exercise any right or remedy it may have against LLC or any
other person without affecting or impairing in any way the liability of either
Guarantor hereunder, except to the extent the Guarantied Obligations have been
indefeasibly paid, and each Guarantor waives any defense arising out of the
absence, impairment or loss of any right of reimbursement or subrogation or any
other right or remedy of either Guarantor against LLC, whether resulting from
such election by MAG or otherwise. Each Guarantor hereby waives, to the fullest
extent permitted by law, all rights and benefits under any applicable law
purporting to reduce a guarantor's obligations in proportion to the obligation
of the principal. Each Guarantor hereby waives any defense based upon or arising
by reason of: (a) any lack of authority of any officer, director or any other
person acting or purporting to act on behalf of LLC, or any defect in the
formation of LLC; (b) any act or omission by LLC which directly or indirectly
results in or aids the discharge of LLC or any Guarantied Obligations by
operation of law or otherwise; or (c) any modification of the Guarantied
Obligations, in any form whatsoever, including without limitation the renewal,
extension, acceleration or other change in time for payment or performance of
the Guarantied Obligations, any waiver or modification of conditions precedent
or any other change in the terms of the Guarantied Obligations or any part
thereof Each Guarantor hereby waives all presentments, demands for performance,
notices of nonperformance, protest, notices of protest, notices of dishonor and
notices of acceptance of this Guaranty and of the existence, creation or
incurring of new or additional obligations. Each Guarantor assumes the
responsibility for being and keeping itself informed of the financial condition
of LLC and of all other circumstances bearing upon the risk of nonpayment or
nonperformance by LLC of the Guarantied Obligations which diligent inquiry would
reveal, represents that it has adequate means of obtaining such financial
information from LLC on a continuing basis, and agrees that MAG shall have no
duty to advise either Guarantor of information known to it regarding such
condition or any such circumstances. Each Guarantor hereby waives notice of any
action taken or omitted by MAG in reliance hereon, and any requirement that MAG
be diligent and prompt in making demands hereunder, notice of any waiver or
amendment of any terms and conditions of the Operating Agreement or Note, notice
of any default by LLC or the assertion of any right of MAG hereunder, any right
to plead or assert any election of remedies in any action to enforce this
Guaranty in respect of its obligations hereunder.

     Section 2.5. Bankruptcy Not Discharge. Notwithstanding anything to the
contrary herein contained, this Guaranty shall continue to be effective or
reinstated, as the case may be, if at any time payment, or any part thereof, of
any or all of the Guarantied Obligations is rescinded or must otherwise be
restored or returned by MAG upon the insolvency, bankruptcy or reorganization of
LLC. Notwithstanding any modification, discharge or extension of the Guarantied
Obligations or any amendment, waiver, modification, stay or cure of MAG's rights

                                       3
<PAGE>

which may occur in any bankruptcy or reorganization case or proceeding
concerning LLC, whether permanent or temporary, and whether or not assented to
by MAG, each Guarantor hereby agrees that it shall be obligated hereunder to pay
and perform the Guarantied Obligations and discharge its other obligations in
accordance with the terms of the Guarantied Obligations as set forth in this
Guaranty in effect on the date hereof Each Guarantor understands and
acknowledges that by virtue of this Guaranty, it has specifically assumed any
and all risks of a bankruptcy or reorganization case or proceeding with respect
to LLC.

     Section 2.6. Guarantors' Understandings With Respect To Waivers. Guarantors
warrant and agree that each of the waivers set forth above is made with such
Guarantor's full knowledge of its significance and consequences and made after
the opportunity to consult with counsel of its own choosing, and that under the
circumstances, the waivers are reasonable and not contrary to public policy or
law. If any of said waivers are determined to be contrary to any applicable law
or public policy, such waiver shall be effective only to the extent permitted by
law.

                                  ARTICLE 111
                              SENIORITY OF NOTE:
                             SUBROGATION: SECURITY

     Section 3.1. Seniority. The obligations of LLC under the Note, and the
obligations of each Guarantor under this Guaranty, shall be senior to all other
Indebtedness of LLC and each Guarantor, respectively, except for (i) existing
Indebtedness of each Guarantor; (ii) Replacement Indebtedness of each Guarantor;
(iii) Indebtedness of LLC (which may be guaranteed by either Guarantor) incurred
for the purpose of acquiring equipment for the Restaurant (as defined in the
Operating Agreement) prior to the date the Restaurant opens for business or
Indebtedness incurred by LLC (which may be guaranteed by Guarantor) permitted by
the Operating Agreement for the purpose of acquiring additional equipment for
the Restaurant, (iv) Indebtedness of either Guarantor incurred to acquire
equipment for additional restaurants opened after the date hereof, or(v)
Indebtedness of either Guarantor incurred on a non-recourse basis in connection
with assets acquired by such Guarantor after the date hereof for which the
obligations are limited to such assets (the "Excluded Indebtedness"). For
purposes hereof, Indebtedness means at any date any of the following: (i) all
obligations, unconditional or contingent, for borrowed money including, without
limitation, principal, interest, premium, penalties and costs (including for
this purpose all obligations incurred under Capitalized Leases), or obligations
evidenced by bonds, notes, debentures or similar instruments; and (ii) all
obligations to pay the balance deferred and unpaid of the purchase price of any
business, real property, other assets or interests therein, except any such
balance that constitutes a trade payable arising in the ordinary course of
business. For purposes hereof, (i) "Capitalized Lease" means a lease of real or
personal property which, in accordance with generally accepted accounting
principles, has been or should have been capitalized by LLC or either Guarantor;
and (ii) "interest" includes, without limitation, interest which may accrue
subsequent to the filing of a petition for relief in bankruptcy or subsequent to
LLC or either Guarantor becoming subject to any other federal or state debtor
relief statute. Neither Guarantor shall incur any Indebtedness from and after
the date of this Guaranty, except for Excluded Indebtedness, which is not either
expressly subordinated to the obligations contained in this Guaranty, or junior
to such obligations by reason of priority established by the security for this
Guaranty granted to MAG. "Replacement Indebtedness" means Indebtedness

                                       4
<PAGE>

incurred to reimburse existing Indebtedness of Guarantors in the aggregate
amount for both Guarantors not to exceed Three Million Two Hundred Thirty-nine
Thousand Five Hundred Dollars ($3,239,500), inclusive of any line of credit, and
upon terms not materially more onerous than existing Indebtedness of Guarantors
comprising that amount.

     Section 3.2. Subrogation. Until the Guarantied Obligations shall have been
paid in full, each Guarantor shall withhold exercise of (a) any claim, right or
remedy, direct or indirect, that such Guarantor now has or may hereafter have
against LLC or any of its assets in connection with this Guaranty or the
performance by either Guarantor of its obligations hereunder, in each case
whether such claim, right or remedy arises in equity, under contract, by statute
(including without limitation under California Civil Code Sections 2847, 2848 or
2849), under common law or otherwise and including without limitation (i) any
right of subrogation, reimbursement or indemnification that either Guarantor now
has or may hereafter have against LLC, and (ii) any right to enforce, or to
participate in, any claim, right or remedy that MAG now has or may hereafter
have against LLC, except for GCI's rights to a Management Fee as provided for in
the Operating Agreement, subject to the subordination of such rights, as
provided for in the Operating Agreement.

     Section 3.3. Security. Each Guarantor, as security for the performance of
its obligations under this Guaranty, hereby grants to MAG a security interest in
all of the properties now owned or hereafter acquired by such Guarantor (except
for properties the subject of Excluded Indebtedness) as more particularly
described in, and pursuant to the provisions of, the Security Agreement attached
hereto as Exhibit A.

                                  ARTICLE IV
                                 MISCELLANEOUS

     Section 4.1. Survival of Warranties. All representations, warranties,
covenants and agreements of each Guarantor contained herein shall survive the
execution and delivery of this Guaranty and shall be deemed made continuously,
and shall continue in full force and effect, until the termination of this
Guaranty.

     Section 4.2. No Waiver. No waiver, forbearance, failure or delay by MAG in
exercising, or in beginning to exercise, any right, power or remedy, nor any
simultaneous or later exercise thereof, shall constitute a waiver of MAG's
rights hereunder, and every right, power or remedy of MAG shall continue in full
force and effect until such right, power or remedy is specifically waived in
writing. No single or partial exercise of any right, power or remedy by MAG
shall preclude any other or further exercise thereof or the exercise of any
other right, power or remedy. All remedies hereunder are cumulative and are not
exclusive of any other remedies that may be available to MAG at law, in equity,
or otherwise.

     Section 4.3. Notices. All notices, requests, demands, claims and other
communications hereunder shall be in writing. Any notice, request, demand,
claim, or other communication hereunder shall be deemed duly given (i) if
personally delivered, when so delivered, (ii) if mailed, two Business Days after
having been sent by registered or certified mail, return receipt requested,
postage prepaid and addressed to the intended recipient as set forth below,
(iii) if

                                       5
<PAGE>

given by telecopier, once such notice or other communication is transmitted to
the telecopier number specified below and the appropriate answer back or
telephonic confirmation is received, or (iv) if sent through an overnight
delivery service in circumstances to which such service guarantees next day
delivery, the day following being so sent:

     If to GCI or GCICA: Grill Concepts, Inc.

     11661 San Vicente Boulevard, Suite 404
     Los Angeles, CA 90049
     Attention: Robert Spivak, President
     Telecopier No.: 310/820-6530

     with a copy to:

     Herzog, Fisher & Grayson
     9460 Wilshire Boulevard, Fifth Floor
     Beverly Hills, CA 90212
     Attention: Michael Grayson, Esq.
     Telecopier No.: 310/278-5430

     If to LLC:

     Chicago - The Grill on the Alley
     ---c/o Grill Concepts, Inc.
     11661 San Vicente Boulevard, Suite 404
     Los Angeles, CA 90049
     Attention: Robert Spivak, President
     Telecopier No.: 310/820-6530

     with a copy to:

     Herzog, Fisher, Grayson & Wolfe, A Law Corporation
     9460 Wilshire Boulevard, Fifth Floor
     Beverly Hills, CA 90212
     Attention: Michael Grayson, Esq.
     Telecopier No.: 310/278-5430

     If to MAG:

     The Michigan Avenue Group
     c/o Albert Sarnoff
     75 Rockefeller Plaza
     New York, NY 10019
     Telecopier No.:

                                       6
<PAGE>

     with a copy to:

     The Michigan Avenue Group
     c/o Wolff-DiNapoli LLC
     11828 La Grange Avenue, Second Floor
     Los Angeles, CA 90025
     Attention: Patricia M. Knott
     Telecopier No.: 310/477-2522

     with a copy to:

     Greenberg Glusker Fields Claman & Machtinger LLP
     1900 Avenue of the Stars, Suite 2100
     Los Angeles, CA 90067-4590
     Attention: C. Bruce Levine, Esq.
     Telecopier No.: 310/553-0687

Any party may give any notice, request, demand, claim or other communication
hereunder using any other means (including ordinary mail or electronic mail),
but no such notice, request, demand, claim or other communication shall be
deemed to have been duly given unless and until it actually is received by the
individual for whom it is intended. Any party may change the address to which
notices, requests, demands, claims and other communications hereunder are to be
delivered by giving the other parties notice in the manner herein set forth.

     Section 4.4. Severability. Any provision of this Guaranty which is
prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction,
be ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof or thereof or affecting the
validity or enforceability of such provision in any other jurisdictions.

     Section 4.5. Governing Law: Jurisdiction. This Guaranty shall be governed
by and construed in accordance with the substantive laws of the State of
California and the United States of America without regard to any law which
would result in the selection or application of the law of any other
jurisdiction.

     Section 4.6. Binding Effect: Assignment. This Guaranty shall be binding
upon and inure to the benefit of MAG and each Guarantor and their respective
successors and assigns, provided that neither Guarantor shall have the right to
assign its rights and obligations hereunder without the prior written consent of
MAG (and any attempted assignment in contravention of the terms hereof shall be
void). This Guaranty shall, without further reference, pass to, and may be
relied on and enforced by, any successor or assignee of MAG.

     Section 4.7. Headings. Article and Section headings in this Guaranty are
included herein for the convenience of reference only and shall not constitute a
part of this Guaranty for any other purpose.

                                       7
<PAGE>

     Section 4.8. Arbitration.

     (a) Any dispute or difference between the parties arising out of this
Guaranty which the parties are unable to resolve themselves shall be submitted
to and resolved by arbitration as herein provided. Either a Guarantor (on behalf
of itself or LLC) or MAG may request the American Arbitration Association (the
"AAA") to designate one arbitrator, who shall be a retired California Superior
Court or Court of Appeals judge.

     (b) The arbitrator shall consider the dispute at issue at Los Angeles,
California at a mutually agreed upon time within sixty (60) days (or such longer
period as may be acceptable to Guarantors and MAG) of the designation of the
arbitrator. The arbitration proceeding shall be held in accordance with the
rules for commercial arbitration of the AAA in effect on the date of the initial
request by Guarantors or MAG, as the case may be, that gave rise to the dispute
to be arbitrated (as such rules are modified by the terms of this Guaranty or
may be further modified by mutual agreement of Guarantors and MAG) and shall
include an opportunity for the parties to conduct discovery in accordance with
California Code of Civil Procedure Section 1283.05, as amended, in advance of
the proceeding. Notwithstanding the foregoing, the parties hereto agree that
they will attempt, and they intend that they and the arbitrator should use their
best efforts in that attempt, to conclude the arbitration proceeding and have a
final decision from the arbitrator within 120 days from the date of selection of
the arbitrator; provided, however, that the arbitrator shall be entitled to
extend such 120-day period for one or more additional 1 20-day periods. The
arbitrator shall immediately deliver a written award with respect to the dispute
to each of the parties, who shall promptly act in accordance therewith. Each
party to such arbitration agrees that any award of the arbitrator shall be
final, conclusive and binding and that they will not contest any action by any
other party thereto in accordance with an award of the arbitrator. It is
specifically understood and agreed that any party may enforce any award rendered
pursuant to the arbitration provisions of this Section 4.8 by bringing suit in
any court of competent jurisdiction.

     (c) Neither this agreement to arbitrate nor any demand for arbitration
hereunder shall waive any party's right to obtain any provisional remedy,
including, without limiting the generality of the foregoing, injunctive relief,
from any court of competent jurisdiction, as may be necessary in such party's
sole and subjective judgment, with respect to matters otherwise subject to
arbitration pursuant to the terms of this Guaranty. However, if either party
seeks or obtains such provisional remedy, an arbitration hereunder shall also be
commenced, and, if necessary, the merits of the controversy or claim and/or the
determination of an appropriate permanent remedy shall be settled by arbitration
in accordance with this Guaranty.

     (d) All fees, costs and expenses (including reasonable attorneys' fees and
expenses) incurred by the party that prevails in any such arbitration commenced
pursuant to this Section 4.8 or any judicial action or proceeding seeking to
enforce the agreement to arbitrate disputes as set forth in this Section 4.8, or
seeking provisional remedies as authorized by this Section 4.8, or seeking to
enforce any order or award of any arbitration commenced pursuant to this Section
4.8 may be assessed against the party or parties that do not prevail in such
arbitration in such manner as the arbitrator or the court in such judicial
action, as the case may be, may determine to be appropriate under the
circumstances. All costs and expenses attributable to the arbitrator shall be
allocated among the parties to the arbitration in such manner as the arbitrator
shall determine to be appropriate under the circumstances.

                                       8
<PAGE>

     Section 4.9. Entire Agreement. This Guaranty constitutes the entire
agreement and understanding between the parties pertaining to the subject matter
hereof and supersedes all prior or contemporaneous drafts, agreements,
representations and understandings of the parties. Each party acknowledges that
it has expressly bargained for a prohibition of any implied or oral amendments
or modifications of any kind, nature or character. Each party agrees and
acknowledges that this Guaranty is fully integrated and not in need of parol
evidence in order to reflect the intentions of the parties, and that the parties
intend the literal words of this Guaranty to govern the transactions described
herein, and for all prior negotiations, drafts and other extraneous
communications to have no significance or evidentiary effect whatsoever.

     Section 4.10. Counterparts. This Guaranty may be executed in counterparts,
each of which shall be deemed to be an original, but all of which taken together
shall constitute but one and the same instrument.

     IN WITNESS WHEREOF, this Guaranty has been entered into by the undersigned
as of the date and year first above written.

"GUARANTOR"

GRILL CONCEPTS, INC., a Delaware corporation

By: /s/ Robert Spivak,
Robert Spivak, President

By: /s/ Michael Weinstock
Michael Weinstock, Secretary

GRILL CONCEPTS, INC., a California corporation

By: /s/ Robert Spivak
Robert Spivak, President

By: /s/ Michael Weinstock
Michael Weinstock, Secretary

                                       9