Roger Federer's ATP World Finals campaign ends amid rumours of feud Roger Federer has been forced to withdraw from the ATP World Tour Finals decider due to a back injury, leaving to Novak Djokovic to be crowned champion without even working up a sweat. Switzerland's Rodger Federer pulled out of the STP Finals amid rumours of a feud with compatriot Stan Wawrinka. THE mystery surrounding Roger Federer's sudden back injury has deepened after John McEnroe claims a post-match argument between Federer and Swiss teammate Stan Wawrinka was a contributing factor in Federer's withdrawal from Barclays ATP World Tour Final. Federer, 33, was due to clash with world No. 1 Novak Djokovic in a Wimbledon final rematch, but withdrew only minutes before the final was due to start. Commentating on ESPN, McEnroe fuelled rumours of a post-match stoush between Federer and Wawrinka - only days out from the start of Switzerland's Davis Cup final clash with France in Lille. "Something went on in the locker room, there was a long talk between the players that extended well into the night," McEnroe said. And the stress of that - I can't confirm all of this - but a lot of this went on and ... I don't think that helped the situation. Federer was said to be upset with aspects of Wawrinka's behaviour - and his support crew - during a gruelling three-set semi-final on Saturday night. The grand slam record-holder is said to have raised the issue with Australian Open champion Wawrinka as the players walked from court back to their individual locker-rooms. The conversation reputedly continued for some time and it was not until well after midnight that Federer returned to his city hotel. Rodger Federer is through to the final of the ATP World Tour Finals after beating compatriot Stan Wawrinka 4-6, 7-5, 7-6. He failed to practise ahead of the final before telling the capacity crowd he could not play. "Unfortunately I'm not match fit to play match tonight," he said. Clearly I wish it wasn't this way. You try all year to be ready for the ATP World Tour Finals and I didn't want to end this way. I tried everything I could last night and today - painkillers, rest - until the very end, but I can't compete at this level with Novak. In a final like this and at my age, it would be too risky. I hope you understand. Djokovic was awarded a walkover - and his fourth season-ending title - when Federer withdrew. It is not known if world No 2 Federer will recover in time for the Davis Cup final. Djokovic played an exhibition set against Andy Murray before partnering McEnroe in doubles against Murray and Pat Cash. Americans Bob and Mike Bryan won the doubles title 6-7 (5-7) 6-2 10-7 against Croat Ivan Dodig and Brazilian Marcelo Melo. It is the fourth time the twins have won the ATP World Tour Final. The Bryans have now amassed a record 103 titles. Originally published as Did feud end Federer's Finals campaign?