Gilles Muller, who lost against Andy Murray in the quarterfinals of Queen's, said that the British No. 1 has significantly improved this year.
The 32-year-old, who is ranked No. 48, said that he and Murray used to hit when they were teenagers in Spain and he knows the Scot really well.
"He's been playing really well, especially this year he's really been... I think he's back on where he was when he was winning Grand Slams," Muller said. "He's very impressive. Back then I knew he was very talented, but seeing him now, you can see how hard he worked to get there. And he's a good example for being in great shape.
"This has been helping him a lot to win very tough matches. His dedication and his passion for the game is really big, because there is not many guys that work as hard as him."
Muller has never able to crack the Top 30, but says that now he is trying as hard as he can before he retires.
"I have two kids at home and a wife, so I have to make it happen, also," Muller said. "Otherwise it's not worth traveling and leaving them all the time.