Man, old, was suffering (6)
I believe the answer is:
oswald
'man' is the definition.
(I've seen this before)
'old was suffering' is the wordplay.
'suffering' indicates an anagram.
'old'+'was'='oldwas'
'oldwas' is an anagram of 'OSWALD'.
(Other definitions for oswald that I've seen before include "Saint who was a seventh century king of Northumbria" , "Old king" , "JFK's assassin" , "Lee Harvey . . . . . ., assassin of JFK" , "Man" .)