Rafael Nadal pulled out of next week’s ATP Tour Finals in London, so Novak Djokovic will end the year as world number one having returned to the top of the rankings on Monday.

French Open champion Nadal announced that an abdominal muscle problem, which prevented him from playing in the Paris Masters last week, and ankle surgery had forced him to pull out of the season-ending event.

“Unfortunately, I had the abdominal problem in Paris last week and I also have an issue in the ankle joint that has to be removed in the operating room,” the 17-time Grand Slam winner wrote on his Twitter handle.

“This way I hope to be in full condition for next season.”

Nadal won a record-extending 11th French Open title in June and reached the semi-finals both at Wimbledon and the US Open. He was forced to retire mid-way through his US Open semi-final in September due to pain in his right knee and has not been able to play a competitive match since.

“I have done everything possible to reach the end of the season in good condition, both in Paris and London, and I really wanted to play,” Nadal added.

On his ankle problem, Nadal said: “It is true that we knew about it for a long time and from time to time, it bothered me. Since the problem in my abdominal muscle also prevents me from playing in London, we have decided to take advantage of the moment and avoid future problems.”

American John Isner will take the 32-year-old’s place in London when the Finals get underway on Sunday. Kei Nishikori has also been drafted in to replace Argentine Juan Martin del Potro, who pulled out due to a knee injury.

Spaniard Nadal’s withdrawal in Paris meant Djokovic returned to the top of the world rankings. The Serb will become the first player since ATP rankings were introduced in 1973 to end the year at No.1 having been outside the top-20 during the same season.

“Reflecting on what I’ve been through in the last year, it’s quite a phenomenal achievement,” said Djokovic. “And, of course, I’m very, very happy and proud about it.

“Five months ago if you told me that, I would find it a bit difficult to accept. I always believe in myself, but it was highly improbable at that time considering my ranking and the way I played and felt on the court.”

Having missed the second half of the 2017 season because of his troublesome elbow, Djokovic returned at the start of this year, but the injury flared up again at the Australian Open and he decided to have surgery on it.

He was dumped out of the French Open as the 20th seed at the quarter-final stage before embarking on a fine run. Djokovic beat Nadal in a Wimbledon semi-final thriller before ending a two-year Grand Slam drought by defeating Kevin Anderson in the final.

A few weeks later, he beat Del Potro in the final to win the US Open and last month claimed the Shanghai Masters title without dropping a set.

“What Novak has achieved this season has to go down as one of the great sporting comebacks. It’s been a phenomenal return to form that would have been hard to imagine just six months ago,” ATP executive chairman and president Chris Kermode said.

“He fully deserves his return to the number one spot in the ATP Rankings and should be incredibly proud of his exceptional season.”