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 subsidiary indication.
'left' becomes 'l' (common abbreviation).
'in' indicates putting letters inside.
'bar' becomes 'save' (save is a kind of bar**).
'l' inserted inside 'save' is 'slave'.
(Other definitions for slave that I've seen before include "Person who is the property of another", "One bound to serve", "Forced labourer", "Person who is owned by someone", "One in bondage", "Drudge", "Person owned for work", "Person in bondage", "Work excessively hard" and "Person in thraldom".)