Murray had been favourite to beat Roddick in the semi final at Wimbledon
Andy Murray is "stuck playing defensive tennis" and needs to "change his mentality" in order to win Grand Slams, according to top coach Larry Stefanki.
Stefanki works with Andy Roddick, who ended Murray's Wimbledon hopes at the semi-final stage on Friday.
"He has to change his mentality of the way he wants to play this game at the very top level," said Stefanki.
"He is stuck playing defensive tennis only, that was the big difference. I don't think he played enough offence."
Murray had been favourite to beat Roddick and become the first British man to reach a Wimbledon singles final since 1938, but lost in four sets to the American.
"I think the difference was that Murray's second serve was very attackable. That was the plan, to move in and club some second-serve returns," Stefanki said in an interview with Radio Wimbledon.
The 51-year-old has coached John McEnroe, Marcelo Rios, Yevgeny Kafelnikov, and Tim Henman in the past, leading Rios and Kafelnikov to world number one.
However, Stefani turned down a chance to work with Murray three years ago because the coach was not "mentally ready for the baggage" which he felt would have come with the job.
Yet, despite his criticism of the British number one, Stefanki is optimistic that the 22-year-old has got a bright future.
"Beside Roger Federer, he is the best mover in the game. He has the best footwork and he is technically very sound," he said.
"His record is great and he is a very strong-minded kid, and I like that, but he needs to recognise when to play offence. I don't think he sees it while he is playing right now and that's the next step for him.
"He is going to have a great future if he gets to the point of recognising balls to attack and to come into the forecourt and play there rather than 15 feet behind the baseline. He will win a lot of Slams, he is that good a mover.
"I think he has plenty of weapons. He hits the ball as cleanly as anybody but you have to learn when to use them and unload on certain balls and I don't see him doing that."
He has developed a big serve and can move the ball from A to B as well as anybody, he just does not know when to do it
Murray has risen to number three in the world since being outclassed by Rafael Nadal in the Wimbledon quarter-final 12 months ago, and Stefanki insisted with a few tweaks to his game Murray can win Grand Slams.
"Murray has the potential to play a lot more aggressively because he has the foot speed, because he can move the ball very quickly, but he has just chosen not to do that," he said.
"I like Andy Murray a lot and I respect his game. He plays it very smart but I still believe the game is played in the forecourt and at the net in order to win some big titles. He will win some big titles.
"You can get through the juniors just being a pusher, a retriever getting balls back.
"I call it negative tennis and that's not going to win you Slams. You have to have some offensive threat. He has developed a big serve and can move the ball from A to B as well as anybody, he just does not know when to do it."
Stefanki has been working with Roddick since December 2008
Former world number one Roddick, who faces Roger Federer in the Wimbledon final on Sunday, has seen a huge improvement in his fortunes since he started working with Stefanki in December 2008.
And the coach revealed how the former US Open winner has driven himself to regaining his past form.
"He is very determined, he can be stubborn which great athletes always are," he said.
"He wanted to find a way to get better. He felt he was stuck, he didn't feel he was going in the right direction.
"I wanted to hear what he had to say and he said a lot of the right things about coming forward more, and he said 'My return of serve is not very good'.
"These are the things I had noticed over the years that were not up to standard for someone in the top eight.
"We talked about Wimbledon and the US Open being a goal because it takes six months to get things right and he killed himself on the court and on the track."