Federer starts Wimbledon on Monday as the number one seed and defending champion, but the Swiss star no longer carries the same air of invincibility which used to characterise his appearances on the lush lawns of south-west London.
For much of the last decade, just the sight of Federer standing across the net on Centre Court has proved a formidable psychological obstacle for his opponents before the first point had even been played.
Yet there is a growing suspicion on the men's tour that the six-time Wimbledon champion is beginning to show chinks in his armour.
By his own enormously high standards, 2010 has been something of disappointment for Federer.
Since beating Andy Murray to claim his 16th grand slam title in the Australian Open final back in January, Federer has failed to win any of his next seven tournaments.
Most disturbing for Federer was the tame manner of his exit from the French Open.
Federer won the first set of his quarter-final against Robin Soderling but then allowed himself to be bullied out of his rhythm by the Swede, who he had beaten in all 12 of their previous meetings.
It was the first time Federer had failed to reach the semi-final of a grand slam since the 2004 French Open, ending a remarkable sequence of 23 successive last-four appearances.
The 28-year-old looked distracted and uninspired for long periods of that Soderling match and, encouragingly for his main rivals at Wimbledon, it wasn't the first time he has given the impression of being less than fully engaged recently.
From 2004 to 2007, Federer won 315 matches and lost just 24 but in the last two and a half years, he has been beaten 35 times.
While that increase in defeats hasn't stopped Federer adding more grand slam titles to his collection, it is the nature of losses to the likes of Tomas Berdych, Marcos Baghdatis and Nikolay Davydenko, who all ended long losing runs against Federer, which suggested the Swiss is no longer quite so fiercely competitive as he once was.
Federer's French Open exit also cost him the world number one ranking as Rafael Nadal overtook him by winning the Roland Garros crown.
Add to that a surprise defeat to Lleyton Hewitt in the Halle final on Sunday -- just Federer's second loss on grass in 78 matches -- and the picture becomes even more worrying.
French Open champion Nadal is the most likely man to dethrone Federer at Wimbledon.
If Nadal can recapture the form he showed on route to winning at the All England Club in 2008, Federer will have a serious battle on his hands to move level with Pete Sampras and William Renshaw on seven Wimbledon titles.
The man himself still has more than enough about him to prove the doubters wrong, however, and he will always be confident of victory at his favourite grand slam.
"I was unfortunate not to come through (against Hewitt) but the loss does not worry me," Federer said.
"It was a good tournament for me. I've got to ensure I draw the right conclusions for Wimbledon."