Game abandoned after love letter from Greece (5)
I believe the answer is:
'letter from greece' is the definition.
(letter from the Greek alphabet)
'game abandoned after love' is the wordplay.
'abandoned' indicates anagramming the letters (the original order is abandoned).
'after' is a charade indicator (letters next to each other).
'love' becomes 'o' (love means zero in tennis).
'game' with letters rearranged gives 'mega'.
'mega' put after 'o' is 'OMEGA'.
(Other definitions for omega that I've seen before include "in Greece, the limit!" , "symbol of resistance?" , "Final Greek letter" , "End of sequence" , "letter to Greeks" .)