Roger Federer’s career hangs in the balance as Swiss star faces ‘many months’ out of the game due to knee surgery (VIDEO)

20-time Grand Slam winner Roger Federer, 40, faces fears about the future of his career after admitting he has only a "glimmer of hope" to return to his best following the surgery that he says is required to his knee.

Federer hasn't competed on the court since losing his Wimbledon semifinal to Hubert Hurkacz in July, with his knee complaint forcing him to skip this summer's Olympic Games in Tokyo.

There had been speculation that the Swiss ace was targeting this month's US Open for his return, but a video message he posted to his 8.6 million followers on Instagram has ruled that – and any other events in the near future – out.

"I just wanted to give you a bit of an update [on] what’s been going on since Wimbledon. As you can imagine, it's not been simple," Federer announced in the video.

"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.

"I’ll be on crutches for many weeks and also out of the game for many months, so 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."

Invasive surgery such as this is always a last resort for high-level athletes – in particular those in their forties, such as Federer.

But the player who is recognized as one of the sport's all-time greats has already defied the ravages of age in the past, including becoming the oldest world number one in tennis history in 2018.

He says he is fully aware of the risks to his career of undergoing surgery.

"I am realistic, don’t get me wrong," he said. "I know how difficult it is at this age right now to do another surgery and try it.

"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."