Rafael Nadal's coach Carlos Moya has revealed the full extent of a foot injury that's seen the 20-time grand slam champion call time on 2021.
Nadal has announced last week that he will sit out the remainder of the season in order to manage an ongoing complaint with his left foot.
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The 35-year-old had already been forced to miss both Wimbledon and the Tokyo Olympics due to the foot injury, which he picked up during the French Open.
Nadal recently revealed he suffers from 'Muller-Weiss syndrome, which is a rare condition caused by an improperly developed bone.
Moya said Nadal has "been in pain for months", and often couldn't finish practice sessions because the injury flared up so badly.
The condition started for Nadal in 2005 and he has been managing it most of his career, but his coach says it became worse after Nadal's break in 2020.
"But this year the story has changed," Moya told the El Transistor program.
"Many training sessions could not be finished and we had to change the training and reduce the pressure on the foot, thinking of tournaments."
Moya admitted that it was difficult to put a timeframe on Nadal's recovery because there is still much mystery around his foot condition.
"One day we had to finish the training, the next day it is fine," said Moya.
"There is a diagnosis, but it's not apparent what is the best treatment."
Nadal's coach insists that pulling the pin on this season and focusing on the future was the best course of action for his player.
"He has been in pain for months," noted Moya.
"In the final match [against Lloyd Harris at Washington, D.C.], he was practically on one leg.
"Rafa's principal objective is to regain good sensations in the foot and mentally, because hobbling around all year has not helped him on court.
"He started with back pain in Australia and he has played just seven events this season. Had to forfeit Wimbledon, Tokyo, and now the US Open, ATP Finals.
"That's why he has to concentrate on himself, not what's happening on tour."
Rafael Nadal explains big decision
Nadal revealed when he made his announcement last week that it was a decision he didn't take lightly.
"It is a year that I have missed things that matter a lot to me, such as Wimbledon, such as the Olympics, how the United States Open is going to be now, (and) many other events that are also important to me.
— ATP Tour (@atptour) August 20, 2021
"In view of the fact that during the latter year I have not had the ability to train and prepare and compete in the way that I really like to... I came to the conclusion that what I need is time to recover.
"I am (determined) to do whatever it takes to regain the best possible shape, to continue competing for the things that really motivate me and the things that I have done during all these years.
"I am convinced that with the recovery of the foot and obviously a very important daily effort this can be achieved. I will work as hard as I can to make it happen."
Nadal's great rival and fellow 20-times grand slam winner Roger Federer is also out of the US Open and will be sidelined for many months because he needs knee surgery, while reigning champion Dominic Thiem withdrew with a wrist injury.
It means world No.1 Novak Djokovic will go into the tournament as an even shorter-priced favourite to complete the calendar grand slam.
The US Open runs from August 30-September 12.
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