Tennis player has unfinished work (4)
I believe the answer is:
graf
'tennis player' is the definition.
(graf was a tennis player)
'unfinished work' is the wordplay.
'unfinished' means to remove the last letter.
'work' becomes 'graft' (I have seen 'Hard work' mean 'graft' so perhaps 'work' could also mean 'graft').
'graft' with its last letter removed is 'GRAF'.
'has' acts as a link.
(Other definitions for graf that I've seen before include "Steffi --, tennis player" , "Steffi --, tennis champion" , "Noted tennis player" , "German count - German tennis player" , "Seven-times women's Wimbledon champion, b. 1969" .)