Tennis great Becker (5)
I believe the answer is:
boris
'tennis great becker' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for boris that I've seen before include "Leading Brexiteer's given name" , "Russian name" , "- Godunov, Russian tsar" , "-- Godunov; -- Johnson" , "Pasternak, perhaps" .)