Roger Federer has revealed he faces “many months” out of the game as he prepares to undergo further knee surgery.

The 40-year-old, who missed the Tokyo Olympics with a knee injury after losing in the quarter-finals of Wimbledon, said he had opted for another operation to give himself “a glimmer of hope” of returning to competition.

“I’ll be on crutches for many weeks and also out of the game for many months,” he said in a video on Instagram on Sunday evening.

He added: “It’s going to be difficult of course in some ways, but at the same time I know it’s the right thing to do because I want to be healthy, I want to be running around later as well again and I want to give myself a glimmer of hope to return to the tour in some shape or form.

“I am realistic. Don’t get me wrong, I know how difficult it is at this age to do another surgery and try it. 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.