Andy Murray is "stuck playing defensive tennis" and needs to "change his mentality" to win Grand Slam titles.

That is the verdict of top coach Larry Stefanki, the man behind former world number one Andy Roddick, who ended Murray's dreams of Wimbledon glory on Friday.

Murray was a hot favourite to beat Roddick in the semi-finals and become the first British man to reach the Wimbledon final since 1938, but lost in four sets to the inspired 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.

"I don't think Murray transitions to offence well enough. He is stuck playing defensive tennis only and, in my opinion, that was the big difference. I don't think Murray played enough offence yesterday.

"Besides Roger Federer he is the best mover in the game. He has the best footwork and he is technically very sound. He has to change his mentality of the way he wants to play this game at the very top level.

"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 of 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."

Stefanki, who turned down a chance to coach Murray three years ago because he was not "mentally ready for the baggage" which would have come with the job, added: "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.

"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.

"I like Andy Murray a lot and I respect his game. He says 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."

As for Roddick, Stefanki also revealed how the former US Open pushed himself to the limit to lose weight when they began working together.

"He is very determined, he can be stubborn which great athletes always are," the 51-year-old added.

"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 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."