Roger Federer
Federer pulled out of the final just hours before taking on Novak Djokovic.Getty Images

Roger Federer has sensationally withdrawn from the final of the ATP World Tour Finals with a back injury just minutes before taking on Novak Djokovic in London.

The 33 year old, who will bid for a first Davis Cup with Switzerland against France next week, suffered a recurrence of a back injury in the third set of his grueling victory over fellow-countryman Stanislas Wawrinka on Saturday.

The decision sees Djokovic crowned as the season-tour finals champion for a third straight year, which caps a fabulous year for the Serbian which also saw him secure the year-end world No.1 for a third time in four years.

"I am not match fit to play the match," said Federer. "I didn't want it to end this way. I've been getting pain-killers and treatment but I can't compete with Novak. I hope you [the crowd] understand."

The 17-time grand slam champion added on his official Facebook page: "I am sorry to announce that I cannot play the finals tonight vs. Novak. I hurt my back late in the match yesterday against Stan. I am very disappointed and I hope to be feeling better soon.

"It's been an extremely difficult decision because I love playing in London and the ATP World Tour Finals have been an absolute highlight of my career. Unfortunately, my back problem does not allow me to play right now. I hope all tennis fans and those involved in the event will understand."

"Clearly this is not the way [I wanted to win]," Djokovic said. "I feel sorry for Roger. I've known him for a long time and Rafa [Nadal] and Roger have been the biggest, most competitive and the guy will always give 100% and if he had come out he would have so I wish him all the best.

"He has an important week ahead of him and obviously I am disappointed for the crowd. This was meant to be an anticipated match between the No.1 and No.2 in the world. I am sure everyone was excited to see it. This is the first time in history that we've had something like this happen.

"It is hard to talk about this achievement. I don't celebrate this particular win."

The scheduled final will be replaced by an exhibition first-to-eight pro-set between Djokovic and Andy Murray, before the Briton teams up John McEnroe to face Tim Henman and Pat Cash in a legends doubles match.

The walkover, just the third time in Federer's professional career that he has pulled out of a match, throws into major doubt his fitness for next weeks' Davis Cup final in Lille, particularly given the world No.2 history with injuries of that nature.