Doubtful individual (7)
I believe the answer is:
sceptic
'doubtful individual?' is the definition.
'sceptic' can be an answer for 'individual?' (sceptic is a kind of individual). I also know that 'doubtful' relates to this answer.
This is the entire clue.
(Other definitions for sceptic that I've seen before include "One might doubt it" , "One inclined to question accepted opinions" , "Person who doubts the truth" , "One questioning accepted opinions" , "One who doubts the truth of religions" .)