John McEnroe says it's "beyond belief" Roger Federer can play the way he does at the age of 36 as the Swiss legend looks to recapture the world No 1 spot in Rotterdam five years after he reached the pinnacle.
The Swiss star can become the oldest-ever No 1 with a run to the semi-finals of the ABN AMRO World Tennis Tournament in the Netherlands.
Federer was sidelined for a significant period in 2016 with a knee injury and upon his return in 2017, he competed in just 12 tournaments and the move appears to have paid off as he stormed to two more Grand Slam titles before winning a landmark 20th major at the Australian Open last month.
"It's still beyond belief and one of the craziest things that I've ever seen in the 25 years that I've been doing commentary and the additional 15 I played to see a guy at that age and that level and play better than he did, for me, at 28," said McEnroe.
"I don't understand how the hell he's doing it, but it's truly amazing to watch."
The American seven-time Grand Slam champion says Federer doesn't put a lot of strain on his body which makes him such a unique individual and displays his joy for the game every time he steps out on the court.
"If you were to pick one thing which I was jealous about would be his absolute love and joy to be out there playing," added McEnroe. "He has this unique ability even during times of struggle to brush things off more easily and that's an incredible quality to have."
Federer is set to play Belgian Ruben Bemelmans in the opening round of the event in Rotterdam on Wednesday.
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