|ATP World Tour Finals|
|Venue: O2 Arena, London Dates: 11-18 November|
|Coverage: Follow live coverage across BBC TV, radio, the BBC Sport website & mobile app. Live text commentary available on select matches.|
Rafael Nadal will miss November's season-ending ATP Finals in London and have surgery on an ankle injury.
Nadal withdrew from last month's Paris Masters with an abdominal muscle injury, meaning Novak Djokovic replaced him as world number one.
The Spaniard, 32, said that since he was still suffering with that injury, he would "take advantage of the moment" and have an operation on his ankle.
American John Isner takes Nadal's place at the eight-player event in London.
|Round-robin groups (world ranking in brackets)|
|Group Guga Kuerten||Group Lleyton Hewitt|
|Novak Djokovic (1)||Roger Federer (3)|
|Alexander Zverev (5)||Kevin Anderson (6)|
|Marin Cilic (7)||Dominic Thiem (8)|
|John Isner (10)||Kei Nishikori (9)|
In a post on social media, 17-time Grand Slam champion Nadal wrote: "It has been a complicated year, very good at the tennis level when I was able to play, and at the same time very bad as far as injuries are concerned.
"Unfortunately, I had the abdominal problem in Paris last week and, in addition, I have a free body in the ankle joint that has to be removed in the operating room today.
"It is true that we had detected it for a long time and from time to time it bothered me. However, since the problem in the abdominal muscle also prevents me from playing in London, we take advantage of the moment to remove the free body and avoid future problems.
"This way I hope to be in full condition for the next season."
Nadal has retired from two of the three hard-court events he has competed at this season - the Australian Open and the US Open - but won the other, the Rogers Cup.
The Spaniard's absence from London means 14-time Grand Slam champion Djokovic will end the year as the world number one for the fifth time in his career: level with Roger Federer and Jimmy Connors, and one behind Pete Sampras.
BBC tennis correspondent Russell Fuller
Nadal has only been able to take up his hard won place at the Finals three times in the past seven years - and last season was far from fit as he pulled out after just one match.
Any year in which you win an 11th title at Roland Garros, Barcelona and Monte Carlo is hardly a wasted one, and yet this has been a deeply frustrating year for Nadal.
He has had to pull out of 10 tournaments for a combination of hip, knee, stomach and ankle problems, as well as fatigue, and also had to retire through injury in his Australian Open quarter-final and US Open semi-final.
As Nadal looks ahead to eight weeks of preparation for the new season, Novak Djokovic now knows he will end the year as the world number one for the fifth time in his career.