Injury cloud over Nadal vs Federer clash at ATP World Tour Finals

Rafael Nadal and Roger Federer can set up a dream climax to the 2017 season at the ATP World Tour Finals, but organisers are sweating on the Spaniard's fitness and a new crop are itching to spoil the party. The two all-time greats get star billing in London after each won two Grand Slams and locked down the top two rankings spots as Novak Djokovic and Andy Murray had injury-plagued seasons to forget. (Video courtesy: Perform)