World No 1 Rafael Nadal faces a fight to be fit for the ATP Finals after withdrawing from the Paris Masters with a knee injury.
The Spaniard told a news conference ahead of his scheduled quarter-final match against Serbia's Filip Krajinovic on Friday that he was suffering from a problem with his right knee
Nadal had already secured the year-end no 1 ranking having won his second-round match against Hyeon Chung earlier this week.
However, his third-round win over Uruguay's Pablo Cuevas saw him take to the court with his knee heavily strapped before eventually prevailing in three tough sets that have taken their toll and ended his tournament early.
"Being honest with myself, being honest with my opponents, I don't see myself playing three more matches here," the 31-year-old said.
"I have to pull out. Of course, it's a very tough decision for me, especially here in Paris, which has been the most important city in my career without a doubt.
"It's a tough situation but I tried my best. I did one treatment yesterday night to try and play today. I am here to win so if I see that I don't have that chance, it's not a good idea to keep trying.
"It's not about London, it's about the longer term. It is important to play tennis as long as possible.
"I'm going to go back, check again with the doctors [like] I did after Shanghai. Let's see. I'm going to do my treatment. In the past it worked well."
The ATP Finals get underway next Sunday and after a memorable season that has seen him claim two more Grand Slam titles in a season haul of six tournament victories, Nadal was well set to contend in London.
Remarkably it is a tournament that the Spaniard has never won and he now faces an anxious week of rehab to make the field for the eight-man end-of-season finale.
Sky Sports has the action from the final Masters 1000 tournament of the year in Paris all this week.
The Next Gen ATP Finals in Milan and season-ending extravaganza ATP Finals at London's O2 in November end another memorable year which will be covered via our website sky.mnosports.com/tennis with live blogs, reports, and expert analysis as the season reaches its climax.
On the move? Head to our app for mobile devices and iPad, or follow our Twitter account @SkySportsTennis to join in the conversation. Who will win the World Tour Finals this year? Have your say...