Rafael Nadal has withdrawn from the season-ending ATP Finals due to a persistent abdominal injury and will take the time off to have ankle surgery.
The Spaniard lost his place as world number one last week when injury forced him to pull out of the Paris Masters, with Novak Djokovic moving to the top of the rankings.
And Nadal will not get the opportunity to end the year on a high as he will not play in London, citing both last week's abdominal issue and a long-standing ankle problem for his absence.
"It has been a complicated year - very good at the tennis level when I have been able to play and, at the same time, very bad as far as injuries are concerned," Nadal wrote on Twitter.
"I have done everything possible to get to the end of the season in good condition, both to Paris and to London, doing things well, and I really wanted to play.
"Unfortunately, I had the abdominal problem in Paris last week and I also have a free body in the ankle joint that has to be removed in the operating room [on Monday].
"We had detected it for some time and it occasionally bothered me. However, since the problem in the abdominal muscle also prevents me from playing in London, we are taking the time to remove the free body and avoid future problems.
"This way I hope to be in full condition for next season."
Nadal has not featured on the ATP World Tour since retiring in the semi-finals of the US Open in September, also suffering this year with hip and knee problems.
The 32-year-old won the French Open - his 17th grand slam title - but he competed in just three hard-court tournaments in 2018, winning the Rogers Cup while retiring at both the Australian Open and at Flushing Meadows.
Djokovic is set to end the year as number one, having enjoyed a sensational run of results that saw him triumph at Wimbledon and the US Open.
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