Flipping idiots! Man U player's unexplained marks on body (8)
I believe the answer is:
stigmata
'marks on body' is the definition.
'stigmata' can be an answer for 'marks' (I've seen this before). I am not sure about the 'on body' bit.
'flipping idiots man u player's unexplained' is the wordplay.
I cannot really see how this works, but
'man' could be 'mata' and 'mata' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for stigmata that I've seen before include "that oddly makes impression on Francis" , "Mercian king who built dyke" , "Wounds like Christ's" , "Spots" , "Marks resembling Christ's wounds" .)