A man seen in the distance (5)
I believe the answer is:
miles
I believe this clue is a double definition.
'a man' is the first definition.
'the distance' is the second definition.
(I've seen this in another clue)
'seen in' acts as a link.
(Other definitions for miles that I've seen before include "Imperial units of length" , "a long way" , "'But I have promises to keep, and . . . . . to go before I sleep' (Frost)" , "Distance units" .)