Novak Djokovic may have to take at least one set or even win the match in order to reach the semis when he goes up against Tomas Berdych at the World Tour Finals on Thursday. Djokovic is trying to bounce back from a round-robin loss to Roger Federer.

Regardless of what happens in Thursday afternoon’s match between Roger Federer and Kei Nishikori, Novak Djokovic will not have clinched a spot in the World Tour Finals semis when he takes the court for the nightcap against Tomas Berdych.

Djokovic put his London campaign in unexpected doubt by losing to Federer 7-5, 6-2 on Tuesday. If Nishikori beats Federer, Djokovic must beat Berdych. Should Federer defeat Nishikori, the world No. 1 only has to take one set against the Czech. As for Berdych, he will already be eliminated if Nishikori wins.

This will be the 23rd meeting between the two players, with…