Tennis great Lendl (4)
I believe the answer is:
ivan
'tennis great lendl' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ivan that I've seen before include "Russian, say" , "his progress in history was terrible!" , "Fellow" , "First Russian tsar, 1547-84" , "terrible tyrant" .)