Unpaid worker left in bar (5)
I believe the answer is:
Here is my best explanation:
'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", "Bondsman, thrall", "Drudge", "Person who is the property of another", "One in bondage" and "Work excessively hard".)