Enthusiastic about love, duck? (5)
I believe the answer is:
avoid
'duck?' is the definition.
(thesaurus)
'enthusiastic about love' is the wordplay.
'enthusiastic' becomes 'avid' ('avid' can be similar in meaning to 'enthusiastic').
'about' is an insertion indicator.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'avid' enclosing 'o' is 'AVOID'.
(Other definitions for avoid that I've seen before include "Evade - escape" , "Keep away from (someone/something)" , "Duck" , "Run away from" , "Shy away from" .)