Find the right ending to this passage.

Roger Federer has pulled out of Sunday night's final of the ATP World Finals at the 02 Arena against Novak Djokovic. The world No 2, who in the past has had back problems, is said to have felt very stiff following Saturday night's epic semi-final against compatriot Stan Wawrinka, which took two hours and 48 minutes to complete. Federer showed class in coming out onto the court to apologise in person to the crowd for his absence, although he was not specific about  the exact cause of his problem. 'I tried everything, rest, massage but I am not match fit,' he said. 'At this level I could not compete. It would be too risky to do it at my age now. Thank you for your support, it really keeps me going, and congratulations to Novak.'


Djokovic had finished his match by 3.30pm on Saturday while Federer was not done until 11pm because the event runs two separate sessions.