Roger Federer has praised Andy Murray for the way that he has altered his game since breaking into the professional tennis circuit.
The Swiss famously criticised the world number three after losing to him at the Dubai Tennis Championship in 2008, insisting that he would have to "grind it very hard" if he continued to play so passively.
"I don't think he has changed his game a whole lot since the first time I played him and I really thought he would have done," Federer said after that match.
"He is going to have to grind it very hard in the next few years if he is going to play this way. He stands way behind the court. You have to do a lot of running and he tends to wait for the mistakes of his opponent."
However, the 17-time Grand Slam champion now believes that Murray is a dangerous adversary but says that he knows exactly what he is up against.
The pair will confront each other for a place in the final of the Australian Open tomorrow morning.
"I know what to expect; whereas it would be different if I hadn't played him," said Federer. "Because he has changed his game around a bit, he's playing more offensive. I'm looking forward to it.
"That's what matters I think the most for him now - in the moment itself, how offensive can you play when the ball is coming flat and hard into the middle?
"You have to know also when to back off. He's very clever at all these things. He knows how it works. But I think it's especially on the return that you see the biggest significant change in his game overall if you look back now."
Federer lost to Murray in the gold-medal match at last year's Olympic Games in London.
