It's due to love taking wing (5)
I believe the answer is:
owing
'it's due to' is the definition.
(owing money)
'love taking wing' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'taking' is a charade indicator (letters next to each other).
'o'+'wing'='OWING'
(Other definitions for owing that I've seen before include "Unpaid" , "Undischarged" , "This debt has yet to be paid" , "Due to, like debt" , "Unsettled; on account" .)