"I'm very happy for everything", said Nadal, who this year won the French Open and the U.S. Open.
Given the troubles he has faced in staying healthy in recent years, he is perhaps wise to prioritise the long term and skip the World Tour Finals as a precaution, with the hope it allows him to enjoy another strong season next year.
"The knee is always bothering me a little bit but sometimes it's worse", Nadal said on Friday, as quoted by "The Guardian". "It has been an fantastic year". "It means a lot".
Nadal has already made sure he would finish the year on top of the ATP Rankings and thus he will not be expected to push himself too much to feature in the year-ending event in London.
The 16 grand slam title holder picked up the injury in his third round game at the Paris Masters against Pablo Cuevas where he needed some medical assistance during the game to be able to continue.
"If you look at any other male tennis player who has ended the year at least four times as number 1, they do so in patches of three of more years".
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"The only one thing i can say is i'm going to do my treatment and try my best to be playing in London but i cannot talk about this now because it's a day that is tough enough for me to have pulled out from here", said Rafa. 'It's a tough situation, a sad one. Of course, I am going to be playing in London normally, if nothing happens.
Chung broke Nadal back in the ninth game of the first set and held for 5-5.
Marin Cilic and Grigor Dimitrov, who also secured their places in ATP Finals, both came through their opening matches in Paris.
The Serbian will go up against John Isner of the United States in the last four after the big-serving American beat Argentina's Juan Martin del Potro 6-4, 6-7, 6-4.
But it was a disappointing day for South Africa's Kevin Anderson and home favorite Jo-Wilfried Tsonga, as the two contenders for ATP Finals berths were knocked out from the tournament.