Patrick Mouratoglou is a world-renowned tennis coach who has worked with Marcos Baghdatis and Aravane Rezai. His French tennis academy is considered one of the top in the world. He is a frequent contributor to Busted Racquet.
Even if he denies it in front of the press, even if he refuses to talk about a changing of the guard, Roger Federer can't get away from it now: His game is slipping, fast. This isn't to attack his credentials or past but to try and approach the situation with a sober mind, which Federer doesn't want to seem to do. He's still good enough to reach at least the semifinals of the events he's entering but not to put away other top players like Rafael Nadal and Novak Djokovic. What's the problem?
His serve doesn't hurt like it used to. Whereas it was a huge weapon for him, this shot isn't decisive anymore and that's why he now has to play many rallies from the baseline. So Federer is giving up easy points on his service games and can't put on the usual pressure when he returns. He once used to get 10 to 15 aces per match and many more winners (not to mention all the short balls he was getting behind his first serve). Now he's struggling with his serve and it weakens his whole game.
A defensive backhand. If this shot was always his "weakness," it was still way better than many others on the Tour. Nowadays he's abusing the chop, which puts him too often on the defense. Furthermore, this shot has less velocity on it than in years past. It's not low or fast enough. His attacking backhand is often leading to many unforced errors when his rivals stick him on that side, as Djokovic did in the Indian Wells semis.
Slowing stamina. Roger remains — and his fitness trainer should be thanked — one of the quickest players on court. His footwork allows him to quickly turn around on his backhand and to take the ball as early as possible. Yet Federer is now suffering on the long runs during a match; some of his ups and downs can be explained by a general fitness that looks like it's slowing.
Distracted focus. It's one of his biggest issues of the moment. While he can still play some matches at a very high level, he also can play others in which he commits a lot of unforced errors. Federer's fitness may be suspect, but his focus is low enough where it appears to be tough for him to keep the same level of commitment during a whole match. It's enough to beat many players, but it hampers him when he battles the top players, who take advantage when Federer first cracks that door.