Rafael Nadal finished his 2018 season

(AFP) - Rafael Nadal is out of the ATP Finals in London next week after revealing his season has been ended prematurely by injury.

Nadal announced on Facebook that he is to undergo ankle surgery after the abdominal injury which forced him to miss the Paris Masters had also ruled him out of the tournament.

"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 not played since the US Open in September and he was usurped as world No 1 on Monday by Novak Djokovic following the Serbian's run to the final in Paris, where he lost to Karen Khachanov.

The ATP Finals, which start on November 11 are usually contested by the top eight players in the Race to London standings.

Nadal joins Juan Martin del Potro in missing the tournament with injury. Kei Nishikori, the No 9, replaces Del Potro, and now No 10 John Isner will come in for the world No 2.