Over the past couple of years, Federer has seen most of his major tennis records being broken by either Djokovic or Nadal. However, the Swiss' aura and popularity are still extremely high even though he last played a tennis match over a year ago as he continues to recuperate from last year's knee surgery.
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Speaking to Sportsklub, Gilles Muller explained why he considers Federer greater than Nadal and Djokovic.
"If we look at the numbers and the Grand Slams, now it's Rafa. To be completely honest, for me Roger Federer is above all," Muller said. "I think that he raised tennis to a higher level, made it more popular, the prize funds are now this big largely because of him."
The 39-year-old also cited Federer's aesthetic playing style as one of the reasons behind his belief.
"I think the way he played was also spectacular, the most beautiful of all - he made every shot look easy, it was special to watch him," said Muller.
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The former US Open quarterfinalist believes Djokovic will end up with the most Grand Slams. Muller explained that he does not adjudge the GOAT based on numbers alone, which is why he reckons Roger Federer is ahead of Nadal and Djokovic.
"Novak is also a spectacular tennis player and I think he will end up with the most Grand Slam titles, unless something unexpected happens - if everything goes well physically, he will play for a few more years," Muller said. "It would be easiest to look at the numbers, but when we take everything into account, I would put Roger above Rafa and Novak."
Furthermore, Gilles Muller showered praise on Rafael Nadal's resilience, pointing out how the Mallorcan always finds a "way to win."
"Nadal wins matches - no matter how he feels, he manages to find a way to win," added Muller.