Unlucky in love with nothing inside bar (7)
I believe the answer is:
ominous
'unlucky' is the definition.
(thesaurus)
'love with nothing inside bar' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'with' says to put letters next to each other.
'nothing' becomes 'O' (O resembles 0).
'inside' indicates putting letters inside.
'bar' becomes 'minus' (the minus symbol).
'o' going within 'minus' is 'minous'.
'o'+'minous'='OMINOUS'
'in' acts as a link.
(Other definitions for ominous that I've seen before include "Menacing, sinister" , "Looking like trouble ahead" , "Inauspicious" , "Threatening, portending tragedy" , "Portending something bad" .)