He has done it before, and he can do it again. Only this time, Grand Slam glory will be all the more remarkable.

The last time Federer underwent knee surgery, he missed the majority of the 2016 season and slipped out of the top 10 in the ATP Rankings for the first time in 17 years. We all thought the Swiss star was done as an elite, title-winning sportsman.

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Federer withdraws from Australian Open
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Yet, Federer's 2017 season marked a return to Grand Slam wins for the first time since 2012, the most titles since 2007, and his highest win percentage since 2006. The then 35-year-old won both the Australian Open and Wimbledon to prove he was very much still in his prime.

However, Federer has again undergone knee surgery, meaning he will miss the upcoming Australian Open. Turning 40 next year, returning to the top after further surgery will be the tallest of orders - can he do it?

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What happened?

Federer had been cautiously optimistic he would be fit for the Australian Open. Speaking back in October, the Swiss was positive but remained wary of his limitations.

"I'm on the right track," he said. "But I don't want to put pressure on myself and take my time. I will only enter tournaments when I am 100 percent fit. At the moment, it looks like I can come back at the Australian Open."

Nonetheless, Federer's agent confirmed the veteran had lost his race to be fit in time for the event at Melbourne Park, even though the tournament has been pushed back to February as a result of the coronavirus pandemic.

“Roger has decided not to play the 2021 Australian Open," Tony Godsick said in a statement.

He has made strong progress in the last couple of months with his knee and his fitness. However, after consultation with his team, he decided that the best decision for him in the long run is to return to competitive tennis after the Australian Open. I will start discussions this coming week for tournaments that begin in late February and then start to build a schedule for the rest of the year.

What is the injury?

Federer has not played since January because of two operations.

In February, Federer had arthroscopic surgery on his right knee. He hoped to return in July, but in June he had another operation that ruled him out for the rest of 2020.

What does this mean for the rest of the season?

In normal circumstances, the French Open would also not be top of Federer's priorities when recuperating from injury.

He missed last year's tournament, and has actually only taken part in one of the last five showpieces at Roland Garros.

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Normally, Federer would perhaps sit out next year's French Open, too, to recover and be fully ready for Wimbledon, but he may think differently in what is likely to be his final year in 2021.

Is this the end?

For almost all of the rest of the tennis playing world, it would mean the end. Approaching 40 on the back of another major surgery would signify the perfect time to call it a day.

But for Federer, giving up is not so easy. Level with his long-time friendly rival Rafael Nadal on 20 Grand Slams, if Federer thinks he is in with a shot of winning one more Slam, he will be back on that court, all guns blazing.

However, this is not like his last comeback. Federer is four years older, and will be without elite-level court time in over a year when, even if, he does return. He cannot be written off, but coming back and even getting to the latter stages of tournaments represents his biggest challenge yet.

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