Announcing the news via video on Instagram, Federer, who will miss the US Open, said: "I will be on crutches for many weeks and also out of the game for many months... I want to give myself a glimmer of hope to return to the tour in some shape or form."
Monday 16 August 2021 13:58, UK
Roger Federer will be sidelined for "many months" because he needs further surgery on a knee injury.
The Swiss, who turned 40 earlier this month, underwent two right knee surgeries in 2020 and has been limited to five tournament appearances this season since his return in March.
Federer pulled out of the Tokyo Olympics, saying he had suffered a setback with his knee during the grass-court season, and his prolonged absence on the tour will see him miss the US Open and Laver Cup.
Announcing the news via video on Instagram, he said: "I will be on crutches for many weeks and also out of the game for many months... I want to give myself a glimmer of hope to return to the tour in some shape or form."
Federer, world No 9, has not played since a quarter-final defeat at Wimbledon last month.
He added: "I've been doing a lot of checks with the doctors as well on my knee, getting all the information as I hurt myself further during the grass-court season and Wimbledon.
"That's just not the way to go forward, so unfortunately, they told me for the medium to long term to feel better, I will need surgery. I decided to do it."
Federer, Rafael Nadal and Novak Djokovic are all tied for the men's record with 20 Grand Slam singles titles.
"I am realistic, don't get me wrong. I know how difficult it is at this age right now to do another surgery and try it," Federer said.
"But I want to be healthy, I will go through the rehab process I think also with a goal while I'm still active, which I think is going to help me during this long period of time."
The US Open - the season's final Grand Slam - begins in New York on August 30.
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