You can see why some people think Andy Murray is grumpy. Watching him on court, he sometimes seems to be followed by a perpetual thick, black cloud; the sort which can turn into a noisy storm when he is not playing as well as the perfectionist in him thinks he ought to be.

There was certainly no ranting or raving yesterday as he patiently and politely went about fulfilling an engagement for his sponsors, David Lloyd Leisure, and found himself surrounded by children. He knows that his on-court intensity means he is often pictured scowling, but he now seems anxious for the public to understand that there is also a side to him that smiles. Judging by the reaction to him at the David Lloyd Centre in South West London yesterday, Murray's young fans seem to rather like him whether he is grumpy or not and since the 20-year-old Scot launched his Allstars campaign two years ago to get under-12s playing tennis, more than 15,000 have signed up in 60 centres across the UK.

"The way I am on the court doesn't necessarily make me that way off it," said Murray. "I think it's normal. It's once you get on the court - it's not about being polite to people, it's about winning tennis matches and that's the most important thing at that time and you go out and do your job the best you can. If that means getting a little bit p***ed off, then I think that's okay because you want to win. The best players expect high standards, and if they are not achieving those high standards, then it's perfectly normal to get annoyed."

Many tennis players are prone to this sort of schizophrenia and can turn from mild to wild the moment the first ball of a match is struck. Murray cites notorious on-court firebrand Lleyton Hewitt as an example, as well as another of his locker-room colleagues, Mikhail Youzhny, who recently got so furious with himself during a match that he smashed himself in the head with his racket and ended up covered in blood.

"That was awesome, I saw that on YouTube," said Murray, with a grin. "I thought the first time I watched it, that he was hitting with his strings and then I slowed it down a few times and it was right on the inside of the frame of the racket. He looked dizzy after he did it. He was bent over. It was awful. I mean, he won the match in the end which is even more amazing. I definitely wouldn't do that . . . those frames are pretty hard. From what I've seen he's a pretty quiet guy, normally."

The same, of course, can be said of Murray, though that should not be mistaken for shyness or, God forbid, a lack of confidence. He is a realist, but one who knows what he is capable of. "I could win Wimbledon this year, it's possible, but I'm not the favourite," he said. "I'd love to win it but you can't say for sure so I'm not going to come out and say I am going to win Wimbledon because there's probably more chance of me not winning it than winning it. But I hope in the future that I'm going to have a better chance and, hopefully, I'm going to give myself every opportunity to do it."

Murray's pragmatic approach to his career also means that he refuses to panic when, as yesterday, his ranking drops. He is down nine places to 22 in this week's ATP Tour standings because he lost early at the Sony Ericsson Open in Miami and so failed to defend the ranking points he earned by reaching the semi-finals of the same tournament last year. The 12-month rolling ranking system can be a friend as well as a foe, though. He did not win a match on clay last season and then injured his wrist in Hamburg in May and was out for four-and-a-half months, which means that the points he lost in Miami were the last he had to defend until August. He is now in the happy position of playing the clay-court season and the British grass events, including Wimbledon, in the knowledge that his ranking is only likely to go up.

Last year's injury problems and a lack of experience on clay at the highest level mean that his record on the surface is poor, which is something he is hoping to change starting with next week's ATP Tour event in Valencia, where he will be accompanied by the two-time French Open champion, Alex Corretja, as well as his regular travelling coach, Miles Maclagan.

Corretja's clay-court nous could be invaluable to a player who has won only four matches on the surface at ATP Tour level, his last coming in September 2006, but there is plenty of raw material to work with since Murray spent more than two years training on the clay-courts of the Sanchez-Casal Academy in Barcelona between the ages of 15 and 17. "It's a question of getting back to some of the basics on clay - things like movement," said Murray. "I think it will work really well."

Corretja will no doubt get to know both sides of Murray over the coming nine weeks, as they build towards the French Open at the end of May. Should the Spaniard have an impact, then Murray will have more reason than ever to show his sunnier side.