Undefeated boxer Laila (3)
I believe the answer is:
ali
'undefeated boxer laila' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ali that I've seen before include "Cassius Clay became Muhammad ..." , "Old fighter" , "Champion boxer" , "Mohammad . . ., . . . Hewson" , ""The Greatest" boxer" .)