Idiot fellow has to cover (6)
I believe the answer is:
clothe
'to cover' is the definition.
('clothe' can be a synonym of 'cover')
'idiot fellow' is the wordplay.
'idiot' becomes 'clot' (I've seen this before).
'fellow' becomes 'he' (I've seen this in other clues).
'clot'+'he'='CLOTHE'
'has' is the link.
(Other definitions for clothe that I've seen before include "Remote area in Mongolia/China" , "Provide with garments" , "robe" , "Invest" , "Dress (someone)" .)