Federer’s withdrawal, which was announced to the crowd after the doubles final and shortly before the singles match was supposed to begin, handed Djokovic a third consecutive title at the tournament.

Federer explained to the crowd in person that he was withdrawing, saying: “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.”

Federer did not leave the O2 Arena until the early hours of this morning and fears about his fitness grew when he failed to show up for a scheduled practice session, not arriving at the venue until around 4pm.

Speaking later, the Swiss said: “It’s a very disappointing end to the season. I was playing so well here, had a great season so far. I was feeling great until yesterday’s tie-break. I felt all of a sudden the back was feeling funny.

“I tried to have treatment on it, medication on it, just tried to turn around as quick as possible really, but I didn’t really feel that much of an improvement overnight.

“Then you don’t have a day off or anything to work with, obviously it’s not enough time to recover. The way I feel right now, there’s no way I can compete at any level really.

“So probably in a few days it’s going to be better, but right now it’s not good enough.”

Federer’s 2013 season was seriously derailed by back problems and fitness has been the key cornerstone of his stellar 2014 campaign.

The 33-year-old’s season is not over, and next weekend’s Davis Cup final in Lille, where he will attempt to win one of the few remaining trophies to elude him, was surely on his mind.

Asked what he would do now, Federer said: “Recovery obviously as quickly as possible, and then travelling to France at some point and getting ready on the clay for the Davis Cup final.”

The news was a huge disappointment for the sell-out crowd but they accepted it with little dissent.

And the mood picked up when they were told the match would be replaced by an exhibition clash between Djokovic and Andy Murray, which the world number one won 8-5.

Murray had been at home in Surrey playing computer games when he received the call at 2pm from ATP executive chairman and president Chris Kermode.

Kermode revealed Murray – who also played in a doubles matches with John McEnroe, Tim Henman and Pat Cash – accepted the invitation immediately and volunteered his services for free.

In a self-deprecating reference to the 6-0 6-1 mauling by Federer that ended his season, Murray joked: “I have to apologise because I clearly pushed Roger so hard on Thursday.”

It is only the third time in his long career that Federer has given an opponent a walkover, while he has never pulled out during a match.

There is a certain irony, meanwhile, that it was the ferocity of the battle between Federer and Wawrinka that caused the problem only a few days before they play together in Davis Cup.

The two are great friends but there was a real edge to the encounter, with Wawrinka appearing to get upset with Federer’s support camp at one point.

Wawrinka shrugged off the incident afterwards but, speaking on ESPN, McEnroe said: “Something went on in the locker room, there was a long talk between the players that extended well into the night.”

Federer’s withdrawal meant Djokovic became the first player since Ivan Lendl in the 1980s to win three consecutive World Tour Finals titles, with the Serbian unbeaten at the O2 since 2011.

The world number one had heard nothing of Federer’s troubles until he was told his opponent had withdrawn during the doubles final, which was won by Bob and Mike Bryan.

“I did my warm-up, obviously prepared for the battle, prepared for a great match as it was anticipated, as the people expected it to be,” said Djokovic.

“It was the last match of the season. I was ready to give it all. I’m sure he was ready, too, to give it all if he could.

“I spoke to him. It’s a question mark for the Davis Cup final, as well.

“I didn’t feel so comfortable again receiving that trophy. Of course, I know that I’ve had a great season and I’m very proud to be holding the trophy. But the way things happened today was definitely awkward.”

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