Diminished man needs a change (8)
I believe the answer is:
lessened
'diminished' is the definition.
(I know that diminished can be written as lessened)
'man needs a change' is the wordplay.
'man' becomes 'les' ().
'a change' indicates anagramming the letters.
'needs' with letters rearranged gives 'sened'.
'les'+'sened'='LESSENED'
(Other definitions for lessened that I've seen before include "Needless (anag.)" , "cut" , "Diminished, decreased" , "belittled" .)