Grumble, as fellow possessing nothing (4)
I believe the answer is:
moan
'grumble' is the definition.
(I've seen this before)
'fellow possessing nothing' is the wordplay.
'fellow' becomes 'man' (fellow can mean a man).
'possessing' is an insertion indicator.
'nothing' becomes 'O' (O resembles 0).
'man' enclosing 'o' is 'MOAN'.
'as' is the link.
(Other definitions for moan that I've seen before include "Beef" , "Complain mournfully" , "Complaint" , "Murmur of pain; grumble" , "Express pain" .)