Vain American embracing tennis player (7)
I believe the answer is:
useless
'vain' is the definition.
(thesaurus)
'american embracing tennis player' is the wordplay.
'american' becomes 'us'.
'embracing' indicates putting letters inside.
'tennis player' becomes 'seles'.
'us' placed around 'seles' is 'USELESS'.
(Other definitions for useless that I've seen before include "Vain - unavailing" , "Of no practical or worthwhile application" , "Ineffective" , "Not worth a jot" , "Not practical or constructive" .)