Main role in ballet is lover I neglected (4)
I believe the answer is:
swan
'main role in ballet' is the definition.
(main role in Swan Lake)
'lover i neglected' is the wordplay.
'lover' becomes 'swain' (old-fashioned term for a lover).
'neglected' is a deletion indicator (neglect can mean to ignore).
'swain' with 'i' removed is 'SWAN'.
'is' is the link.
(Other definitions for swan that I've seen before include "Flighty" , "Mute, whooper or Bewick's bird" , "Sweet name 8 [OF SHAKESPEARE]" , "Bird of Cygnus genus" , "Graceful bird" .)