Seles rival (4)
I believe the answer is:
graf
'seles rival' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for graf that I've seen before include "German tennis player, b. 1969" , "German count - German tennis player" , "Seven-times women's Wimbledon champion, b. 1969" , "Noted tennis player" , "Steffi --, tennis player" .)