Zulu idol losing his first love (4)
I believe the answer is:
zero
'love' is the definition.
(love is zero in tennis)
'zulu idol losing his first' is the wordplay.
'zulu' becomes 'Z' (phonetic alphabet: alpha, bravo, charlie etc.).
'idol' becomes 'hero' (I've seen this before).
'losing' suggests deleting specific letters.
'his first' becomes 'h' (1st letter of 'his').
'hero' with 'h' taken away is 'ero'.
'z'+'ero'='ZERO'
(Other definitions for zero that I've seen before include "See 22" , "Nothing; freezing point (in degrees centigrade)" , "Loser" , "Nonentity" , "Love" .)