A collapsible pouch provided with a closure assembly (10; 110; 210; 310; 410), comprising: - a collapsible pouch having a product chamber between two walls (3,4) of film material, preferably said film material including at least one inner layer of plastic, preferably said pouch being filled with a product, e.g. a food product, - a closure assembly (10; 110; 210; 310; 410) that is sealed between said two walls of the collapsible pouch, wherein the closure assembly comprises: - a monolithic spout base and cap part (11; 111; 311), which part is molded of plastic material, said spout base and cap part comprising a spout base (12; 112; 212; 312; 412) delimiting a bore (13; 113) which extends through the spout base, said bore having a lower opening at one end thereof and an opposed cap side opening, wherein the spout base has a sealing wall having an exterior surface to which said two walls of the collapsible pouch are sealed, said spout base and cap part further comprising a cap (20; 120; 220;320; 420), e.g. a rotational cap, wherein the cap comprises a top wall (21; 121) and a downward depending skirt (22; 122; 222) forming an interior side of the cap and delimiting a cap cavity which is aligned with the bore of the spout body, said skirt having a lower edge remote from the top wall, wherein the cap (20; 120; 220) is, preferably at the lower edge of the skirt, integral with the spout base (12; 122) via an integrally molded frangible zone (25; 125; 225; 325; 425) connecting the cap to the spout base such that the cap is manually removable and upon motion of the cap in an opening direction by the user for the first time the frangible zone breaks, characterized in that the closure assembly is a pre-assembled closure assembly (10; 110; 210; 310; 410) and in addition to the monolithic spout base and cap part (11; 111) comprises a tubular inner part (30; 130; 230; 330; 430), preferably said tubular inner part being molded of plastic material, wherein the inner part (30; 130; 230; 330; 430) comprises a fixation portion (31; 131; 231) and a neck portion (32; 132; 232), which inner part has been inserted into the spout base and cap part (11; 111) via the lower opening of the bore thereof in a pre-assembly operation prior to sealing of the pre-assembled closure assembly between said two walls (3, 4) of the collapsible pouch, wherein the fixation portion (31; 131; 331; 431) is received and fixed in the bore of the spout base (12;112; 212) and wherein the neck portion (32;132) protrudes from the spout base into the cap cavity and extends to a mouth opening (34; 134) of the neck portion, and in that the neck portion (32; 132) is provided with at least one circumferential sealing surface (32a, 32b, 32c; 132a, 132b), and in that the cap has at the interior side thereof at least one circumferential sealing surface (23a, 22b, 22c; 123a) that sealingly engages said at least one circumferential sealing surface of the neck portion. - a collapsible pouch having a product chamber between two walls (3,4) of film material, preferably said film material including at least one inner layer of plastic, preferably said pouch being filled with a product, e.g. a food product, - a closure assembly (10; 110; 210; 310; 410) that is sealed between said two walls of the collapsible pouch, - a monolithic spout base and cap part (11; 111; 311), which part is molded of plastic material,