Unpaid worker left in bar (5)
I believe the answer is:
slave
'unpaid worker' is the definition.
(I've seen this before)
'left in bar' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' is an insertion indicator.
'bar' becomes 'save' (save is a kind of bar**).
'l' inserted into 'save' is 'SLAVE'.
(Other definitions for slave that I've seen before include "Forced labourer" , "One bound to serve" , "Person in bondage" , "Person who is owned by someone" , "Person owned for work" .)