Rafael Nadal has pulled out of the Paris Masters before his quarter-final match, with the Spaniard citing a right knee injury which has bothered him in recent weeks.
Nadal's withdrawal from the last event of the ATP regular season came two days after he claimed his fourth year-end world No.1 ranking.
Nadal was to have faced Serb Filip Krajinovic in the last eight.
Roger Federer, who would have had a chance to overhaul Nadal in Paris, did not play this week as he rests after winning the Basel title; Nadal skipped Basel due to his knee but was judged fit for Paris.
"Its a tough situation, I came here, tried my best, I did all I could to play this event," Nadal told a news conference.
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The 31-year-old said he felt knee pain during his three-set win on Thursday against Pablo Cuevas and took treatment for his problem after playing on to finish the match.
"I was hoping to play today, but it's impossible to go on court. I have to pull out and that's what I did.
"I'm sorry for the tournament and the fans, this is a sad day for me. I came here to try and go as far as I could," he said.
Nadal refused to look ahead to the eight-man starting on November 12 in London.
"This is not the day to talk about London, I've had to pull out in Paris, the most important city of my career. It was a hard decision for me.
"I will do my treatment and try to play London. But it's tough enough for me to have to withdraw here.
"The knee has been bothering me for awhile, it's late in the season and I've played a lot of matches.
"I've pushed the body and this kind of thing can happen. I cannot compete at the standard that I need to."
