Rafael Nadal received treatment to his right knee during his victory over Karen Khachanov
Rafael Nadal has withdrawn from his Indian Wells semi-final against Roger Federer with a right knee injury.
The world number two received treatment to the knee during his gruelling quarter-final win over Russia's Karen Khachanov on Friday.
The Spaniard looked in discomfort during the match and only had a brief practice session on Saturday.
"It's tough for me to accept all these things that I'm going through in my career," Nadal said.
Nadal and Federer, who have 37 Grand Slam titles between them, have not played each other since 2017.
Swiss Federer received a walkover to Sunday's final, where he will play either Austria's Dominic Thiem or Milos Raonic of Canada.
"I warmed up today and I felt that my knee was not good to compete at the level I needed," Nadal said.
"Sometimes I feel sad because I'm in a disadvantage to all my opponents."
It would have been the 39th time Nadal and Federer had played one another, with the Swiss having won the past five matches.
They last met in the final of the Shanghai Masters two years ago, which Federer won 6-4 6-3.
Nadal completed just one hard-court tournament in 2018 - the Rogers Cup in Canada, which he won - because of his injury struggles.
He was forced to retire from his Australian Open quarter-final in January 2018 and again during the semi-finals of the US Open.
The 32-year-old reached the final of this year's Australian Open, where he was beaten in straight sets by Novak Djokovic.
Speaking to reporters after his victory over Khachanov, Nadal said he "could not guarantee how I'm going to wake up tomorrow".
"I love to play on hard, but probably my body doesn't love it that much," he added.
"My feeling is there are a lot of players that love to play on hard, true, but their bodies don't love to play on hard, either."
