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
On the final day of round-robin matches,
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.