Missing from this year's ATP Finals, title holder Jannik Sinner admitted that he's had days on which he could barely move due to the knee injury which has kept him out of action since winning Wimbledon.
Sinner, who was world number one until being displaced by Alexander Zverev earlier this month, recently said that he will make his comeback at the "Six Kings Slam" tournament in Saudi Arabia, which has been rescheduled for late December due to the conflict with Yemen's Houthis.
"I had days where I felt nothing and I could play without any problems and then I had days where I couldn't move at all," Sinner said in a video published on his YouTube channel.
"The worst part for me about this injury is that I cannot compete, I cannot play tennis.
"Also my life outside of tennis is a bit more limited because of a simple fact that I cannot do things that I really like, because I want to protect my knee."
Sinner had been having another superb season before succumbing to his knee injury, and he revealed in the video published Wednesday that tonsil surgery caused him to lose a lot of weight.
Before his knee injury, which prematurely ended his season, Sinner had won five consecutive Masters 1000 tournaments -- Indian Wells, Miami, Monte Carlo, Madrid, and Rome -- to complete his set of top-tier ATP events, before being crowned Wimbledon champion for the second straight year.
"I'm not going to lie, it's also tough to see other players play and I cannot compete," said Sinner.
"Also because the season I've had, it has been an incredible season until the moment when everything happened and it switches from a very very positive season to a very tough ending of season even though I had a lot of success."
Last week Sinner announced that Magnus Norman will replace his long-time coach Darren Cahill, who helped shape the Italian into the world's top tennis player.