Roger Federer was beaten by Andy Murray on Monday but believes the Briton's game has not really changed since they first met on the ATP Tour in 2005.
The world number one first met Murray in the Thailand Open final 2-1/2 years ago when the Briton was ranked 109th.
Although Federer won that contest, Murray has beaten him in their other two encounters.
In the last two seasons, the 20-year-old Murray has claimed five titles but Federer was not very impressed by the world number 11's tactics on Monday.
"I don't think he's changed his game a whole lot since I played him in the Bangkok final," the Swiss said after he was beaten 6-7 6-3 6-4 in the first round of the Dubai Championships by Murray.
"Not that I'm disappointed but I really would have thought he would have changed it in some ways."
Federer added that Murray would have to work very hard to sustain a career at the top of men's tennis.
"It sort of works for him but he's going to have to grind very hard for the next few years if he keeps playing this way," said Federer.
"He stands way far behind on the court and (that means) you've got to do a lot of running, and he tends to wait a lot for the mistake of the opponent.
"I gave him the mistakes today but I think overall, over a 15-year career, you want to look to win a point more often than for the guy (opponent) to miss.
"That's what served me well over the years but who knows, he might surprise us all and do it for 20 years."
Murray was surprised by Federer's comments.
"You do different things against different players." said the Scot.
"You go and watch my match against Rafael Nadal at the (2007) Australian Open, and I was playing pretty close to the baseline in that match and taking a lot of risks because I think that's the right way to play against him," said Murray referring to his five-set defeat by the Spaniard.
"Against Federer I don't think that's the right way to play. I'm not going to play that sort of game against someone that defends as well as Federer does."
He also hit back by highlighting the improvements he has made to his game.
"My serve is clearly much better than it was two years ago," he said. "I feel quicker and stronger around the court. Mentally I feel like I'm better.
"But there are still some things in my game that I want to improve and it does take some time to put them into the match court. I feel like I've started to do that this year." (Reuters)
Federer not impressed by Murray