LONDON: A mouthwatering finale to the season ended before it even began on Sunday when Roger Federer was forced to pull out prior to the ATP World Tour Final showdown with Novak Djokovic.

The 33-year-old Swiss, who spent nearly three hours late on Saturday beating compatriot Stanislas Wawrinka in a gruelling semifinal, announced his decision on court as the O2 Arena filled up for the expected final.

Federer, who was bidding for a seventh title at the year-ender, apologized but said he was not “match-fit” after developing a back problem.

“I hope you understand I wanted to come out personally and excuse myself for not playing ... I can’t compete without a back at this level,” he told the crowd who still warmly applauded, despite their obvious disappointment.

ATP president Chris Kermode, standing alongside Federer, then announced that Andy Murray, who failed to qualify for the semifinals after being thrashed by Federer on Thursday, would play Djokovic in a one-set exhibition match instead.

“Unfortunately I’m not match fit to play match tonight. 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,” six-time Tour Finals champion Federer told the crowd during an on-court interview.

“I’m sorry I’m here in a tracksuit. I wish it weren’t so.

“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.”

The 17-time Grand Slam champion is due to lead Switzerland’s challenge against France in the Davis Cup final, starting in Lille on Friday, and the prospect of missing out on a first title in the team event if he aggravated the back problem against Djokovic may have influenced his decision.

“I hurt my back late in the match yesterday against Stan. I am very disappointed and I hope to be feeling better soon,” Federer said.

“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.”

Sunday’s withdrawal was only the third walkover of Federer’s career.

Speculation of a withdrawal mounted when Federer, who took nearly three hours to defeat Wawrinka in a match that didn’t finish until nearly 11.30pm local time, failed to show up for a scheduled practice session on Sunday afternoon.

The worldNo. 2 then confirmed his decision to pull out following the Bryan brothers’ victory in the doubles final.

With Federer sidelined, Djokovic was awarded the Tour Finals title for the third successive year — making him the first player to achieve that feat since Ivan Lendl in the 1980s.

It was hardly the way the world No. 1 would have wanted to take the silverware however.

Fans were already streaming into the 17,500-capacity south-east London venue when the announcement of Federer’s withdrawal came less than an hour before the scheduled start.