Andre Agassi says a lack of depth isn’t the reason why Roger Federer, Rafael Nadal, Novak Djokovic, and Andy Murray are dominating men's tennis. Since Agassi retired after the 2006 U.S. Open, those four players have combined to win every Grand Slam singles title except for one, and have also won the vast majority of the Masters Series titles.

“You see these guys, the way they move, the way they adapt, the way they fight, and I don’t think it’s a depth issue whatsoever,” Agassi said at the Australian Open. “I also had the luxury of playing against Federer, and that was off the heels of competing against Pete [Sampras]. There’s just no safe place to go on the court. It never leaves your racquet and you’re comfortable. It used to leave my racquet, and I knew exactly to a minute detail how opportunistic I could be about the next shot. With him, it wasn’t the case.  
“I played Nadal. I played lefties who have a lot of spin and like to be on offense if they can. I watched myself cane back against his forehand, and he went up with it and then I would take over the point and then win the point. The next adjustment he had was he just went higher and shorter, so he would push me to commit even further. And then he would play around me up the line. I’m like, ‘What the hell am I looking at here? This is different.’”  
Agassi, who won eight Grand Slam titles, said that world No. 1 Djokovic is effective both offensively and defensively, while one of his rivals, former Roland Garros champion Michael Chang moved well but, “once you have him running, I didn’t care. He’s fast. He’s just going to get to one more ball, but that’s his problem if he wants to run one more time, it’s not mine. And then you see it go to the Lleyton Hewitt who would move even better. But if you just were off on one, he would then move forward in the court and turn a point around. Now you got problems if you don’t keep him on the defense. And then you take that to a guy like Djokovic, who probably even was better than Hewitt ever moved and doesn’t need to turn a point around. When he’s on defense he can actually win the point with one shot. He creates his own set of rules out there.”  
Agassi said the game has quickly evolved and called this a remarkable era. He said that Murray, whom he picked to beat Federer in the Australian Open semifinals, can establish himself amongst the other top players.  
“He’s coming into his own now,” he said. “He believes now, and so now you’re talking about four guys. They’ve separated themselves from the field, and they’ve done it arguably overnight, meaning it’s clear that they raised the stakes. It’s not like this has sort of morphed. If it was one person, I would say, ‘Okay, he came at a good time or he squeezed in a window.’ But they raised each other. Those guys have changed the rules out there.”