Last week, he had to forfeit the tournament of Paris-Bercy due to injury to the abdominal muscles.
Novak Djokovic will begin the week as the top-ranked men's singles player in the world, but it was not the flawless ending he anticipated after suffering a shock loss to Karen Khachanov in the final of the Roles Masters in Paris on Sunday.
As most people expected, Rafael Nadal withdrew from the Nitto ATP Finals on Monday, citing multiple injuries.
The Serbian will now become the first player since ATP rankings were introduced in 1973 to end the year at number one having started it outside the top 20.
On his ankle problem, he said: "It is true that we knew about it for a long time and from time to time it bothered me".
"But unfortunately, I had an abdominal problem in Paris last week and, in addition, I have a [problem] with my right ankle joint that [required] an operation [today]".
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"In this way I hope to be in full condition for the next season. Thank you all for the support".
"I want to talk about how well he played all week", Djokovic said, as per ATP's official site.
But once again, the limelight and the sport's biggest prizes were taken by the holy triad - The Big 3 of Novak Djokovic, Rafael Nadal and Roger Federer.
Novak Djokovic reclaimed the world No.1 ranking on Monday after a two-year absence and is assured of finishing the year there. But he competed in only three events after the French Open in June. Roger Federer has a big serve too'.
The issue was serious enough to also rule Nadal out of the Masters 1000 events in Indian Wells and Miami, but he went on to enjoy familiar success on clay, including yet another French Open title.
Novak Djokovic is the top seed in this group and is pitted against Alexander Zverev, Marin Cilic and John Isner, which on paper definitely looks like the tougher group of the two, especially given the surface and conditions.