Fellow covering miles is a winner (5)
I believe the answer is:
champ
'winner' is the definition.
(I know that champ is a type of winner)
'fellow covering miles' is the wordplay.
'fellow' becomes 'chap' (both can mean a man).
'covering' indicates putting letters inside.
'miles' becomes 'm' (abbreviation).
'chap' placed around 'm' is 'CHAMP'.
'is a' is the link.
(Other definitions for champ that I've seen before include "Gnaw; winner (abbr.)" , "press on a bit?" , "boxer who is top dog?" , "Bite - victor (abbr)" , "first place" .)