Roger Federer, who was upset by Nick Kyrgios in the second round Madrid despite holding match points, says the 20-year-old Australian is already a great player but tneeds more seasoning. Kyrgios lost to John Isner in the next round in three sets.

"He's got a wonderful serve, good potential, so I hope he keeps working hard and that he can compete for the best spots in tennis," Federer said. "He likes the big stage. He's got nothing to lose, no fear, and he's got a great game. He can rely on his serve so much. It keeps him in the match regardless of he how he plays from the baseline. All he needs to do is string a few good shots, a few good points together when it really matters."

The 17-time Grand Slam champion added that while many of the sport's top young players have a tremendous arsenal of shots, they still have a lot of work to do to realize their potential. Federer noted that Novak Djokovic, Rafael Nadal, and Andy Murray all improved over the years, but it took time for them to figure out exactly how to hit the right shots.

"I think both of us probably also needed some time when we were younger to figure out our games," Federer said about himself and Kyrgios. "We have a lot of possibilities in terms of shot selection. To hit the right shot at the right time is something that for us comes a bit more difficult than a steady baseliner who is just happy to rally. We prefer to do other things out there. That's why [Kyrgios] might take a few more years to really crack the code."