Ungenerous to be left in wretchedness (7)
I believe the answer is:
miserly
'ungenerous' is the definition.
('miserly' can be similar in meaning to 'ungenerous')
'left in wretchedness' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' means one lot of letters goes inside another.
'wretchedness' becomes 'misery' ('misery' can be a synonym of 'wretchedness').
'l' going within 'misery' is 'MISERLY'.
'to be' acts as a link.
(Other definitions for miserly that I've seen before include "Stingy" , "Niggardly" , "Mean with money" , "Mean, tight" , "Penny-pinching" .)