Clue: Kick person suffering from overwork (4)
Answer: HACK
Explanation: Kick person suffering from overwork (4)
Double definition, although I think the setter should indicate that the second definition is no longer current. 
Hack is an obsolete word for an overworked person, as in this quote from Goldsmith
 
*Here lies poor Ned Purdon, from misery freed, / Who long was a bookseller's hack