Exploits work's weakling (7)
I believe the answer is:
milksop
'weakling' is the definition.
(I've seen this before)
'exploits work's' is the wordplay.
'exploits' becomes 'milks' (milking is a kind of exploiting).
'work' becomes 'op' (common abbreviation for 'opus').
'milks'+'op'='MILKSOP'
(Other definitions for milksop that I've seen before include "Unmanly man" , "He shrinks from" , "Feeble youth" , "Feeble ineffectual man" , "Cissy (informal) -- limps OK (anag)" .)