Rafael Nadal will have season-ending surgery Nov. 3 for appendicitis, which will keep him out the Paris Masters and the ATP finals in London.
He announced the decision after losing to 17-year-old Borna Coric in the quarterfinals of the Swiss Indoors in Basel.
It's the day to say goodbye to the season," Nadal said. "It's been a very hard year for me, mentally and physically. I'm not going to play Paris and London, I'm not competitive enough for that. I need to do the surgery for my appendix and I need to work on my back.
"I need five weeks of rest and I want to have one month to try to work as much as I can to be ready for 2015. The only way to work on being fit is to be healthy. I need to fix all the things in my body first."
In other matches, top-seeded Roger Federer advanced with a 7-6 (4), 6-2 victory over fifth-seeded Grigor Dimitrov. Coric next plays David Goffin, who beat fourth-seeded Milos Raonic of Canada, 6-7 (3), 6-3, 6-4. Federer next faces Ivo Karlovic.
Serena Williams will meet Caroline Wozniacki in the semifinals of the WTA Finals at Singapore, and Simona Halep will take on Agnieszka Radwanska.
On the final day of round-robin matches, Maria Sharapova, Petra Kvitova and Ana Ivanovic all had control of their destinies but failed to advance. Sharapova needed to beat Radwanska in straight sets but faded after being a set and 5-1 up to lose the second set as she failed on three match points.
Sharapova's elimination, although she prevailed in three sets, gave the year-end No. 1 ranking to Williams. Kvitova needed to beat Wozniacki but lost, 6-2, 6-3. Ivanovic needed to beat Halep in straight sets. She came from two breaks down to win the first set but lost the second.
Top-seeded David Ferrer earned his 600th career win by beating Thomaz Bellucci, 6-1, 6-2, to set up a semifinal against Andy Murray at the Valencia Open in Spain.