Novak Djokovic pulled out of the Paris Masters with a nagging shoulder injury before his quarterfinal against Jo-Wilfried Tsonga on Friday.
The top-ranked Djokovic announced on his website that the injury got worse after his third-round comeback win against fellow Serb Viktor Troicki on Thursday.
"Sadly I have to inform you that I have withdrawn from the tournament. I have pushed myself to the limit by playing, and after the match yesterday my shoulder got worse," Djokovic wrote. "For this reason, I have to put my health first and withdraw even though my urges as a professional player are making me want to play until the last drop of energy."
Djokovic, the 2009 champion, made 44 unforced errors against Troicki, and was clearly impeded from playing his best tennis.
"I am very sorry for all of you who bought tickets and wanted to come and watch me play," Djokovic said. "My season has been long and tiring, I played all of my matches at my highest level, and now my body is aching for recovery."
Tsonga, the 2008 champion, advanced to a semifinal against either David Ferrer of Spain or John Isner of the United States.
Djokovic only just returned to the tour last week after a six-week injury layoff, and his shoulder began to bother him again when he lost in the Basel semifinals, only his fourth defeat all year.
He still decided to compete in Paris, ensuring he earned $1.6 million from the end-of-year ATP bonus pool. Had he withdrawn from Paris, a second successive Masters event, Djokovic would have missed out on the bonus.
Djokovic has had an incredible season, winning 10 titles, including the Australian Open, Wimbledon, and the U.S. Open and a season-record five Masters. He's dominated Rafael Nadal this year to replace the Spaniard as the world's best player.
Nadal pulled out before the tournament.
Djokovic, Nadal and Tsonga have all qualified for the eight-man ATP World Tour Finals which starts in nine days in London.