Murray faces Andy Roddick in today's second semi-final on Centre Court and the British No 1 has been warned by John McEnroe that he had "better be ready".

Roddick holds the record for the fastest serve in the game at 155mph. His fastest serve this tournament is 141mph and so far he has thundered down 139 aces, second only to Ivo Karlovic.

McEnroe said: "Roddick possesses one major weapon in that serve. It's the hardest I've ever seen. At the very least he has a puncher's chance, so Murray had better be ready. Roddick's a smart guy and the pressure being off should help him."

While Roddick's serve is an obvious threat, Murray, whose epic fourth-round encounter against Stanislas Wawrinka attracted 12.6m BBC viewers at its peak, has demonstrated that he has matured into the complete tennis player.

His own first serve has been clocking in at more than 130mph regularly on the speed gun, while his ability to switch defence into devastating attack with the variety of his shot-making has been a major feature of the tournament.

Roddick has traced Murray's rapid rise and puts much of it down to the maturity and experience he gained in defeating Richard Gasquet in a five-set thriller last year.

The American No 1 said: "I think this tournament did wonders for him last year, especially the Gasquet match. He's certainly capable of hitting all the shots. It's just a matter of being able to do it day after day now.

"He doesn't really have a lot of weaknesses. He's improved his serve a lot. He returns well. He has been playing great. He's certainly come into his own."

Roddick reached the Wimbledon final in 2004 and 2005, losing both times to Roger Federer. His one grand slam success came at the 2003 US Open, but while his one-dimensional game appeared to have been left behind by players such as Federer and Rafael Nadal, he proved by reaching the semi-final at the Australian Open in January that he is still a force.

Roddick said: "With my serve, I can give myself a chance in any match. I'm going to have to play well and, hopefully, he would probably say the same."

Scattered showers are forecast for the Wimbledon area today so there is the possibility that the match could take place under the new roof, which would hand Murray a distinct advantage since he sampled the indoor conditions in his match against Wawrinka on Monday.

Murray was negative in his comments about how the humid conditions affected his serve that night but insists he is happy with Wimbledon's £100m new addition.

"You have to alter your game style slightly because it's a slower court but I don't mind if it's indoors or outdoors," said the Scot. "I think it is important if you are going to play under the roof you know half-an-hour in advance. That's all I would ask for which I don't think is unreasonable."

He was much more concerned, however, with guarding against complacency with the hype surrounding his quest to become the first British man to win the Wimbledon singles crown since Fred Perry in 1936.

Murray said: "Roddick is one of the best servers in the game. I'll have to return very well. He's made two finals, been No 1 in the world, been a grand slam champion. It's going to be tough."