Sitting on a sofa in the bar of the Priory tennis club in Birmingham, Maria Sharapova is listening to Alicia Keyes on a mini iPod. Around her, members order tall drinks and swap gossip. Most are unaware that the Wimbledon champion is among them. Those that do recognise the blonde, long-legged teenager keep reverential distance.

　　Sharapova is waiting to go on court at the DFS Classic. It is just over a week before Wimbledon and she has chosen to play in a tournament populated with B-list players, just as she did last year. Sharapova, of course, is A-list, having followed her Wimbledon triumph with victory over Serena Williams to claim the WTA Championship last year. She is ranked second in the world, behind Lindsay Davenport. She steps on to Centre Court on Tuesday as favourite to retain her title.

　　She has chosen Edgbaston precisely because it is low-key. But during the week, at the end of which Sharapova retained her title, there is evident tension during matches and signs of strain off the court. At a planned autograph session with children she fails to make eye contact with her young fans. In post-match press sessions, she seems irritable. And, having been granted just 0 minutes with her for a Wimbledon preview, the BBC's Sue Barker finishes the interview three minutes early because Sharapova is so unresponsive.

　　Her rather weary attitude is hardly surprising, though, because the young woman from Siberia is relentlessly in demand. And not just from fans. On another list that ranks the world's best tennis players, Sharapova also comes in second, and this time her achievement is perhaps more remarkable because the list covers men and women.

　　Only Andre Agassi pulls in more than Sharapova's $22.5 million (?12m) a year from endorsements. Sharapova, whose conventional good looks have gained her a contract with IMG Models, also has deals with Colgate-Palmolive, Nike, Prince, Microsoft, Honda, Pepsi, Motorola, Canon, NEC, Parlux Fragances and TAG Heuer, which make her the world's highest-paid female athlete. The watchmakers are bringing out a 3,000 limited-edition, diamond-encrusted 'Maria Sharapova' model at ?1,000 a pop. She can realistically dream of future earnings to match those of Tiger Woods ($77m last year) and immediately after her defeat of Serena Williams in last year's Wimbledon final, the Russian's projected earnings were $150m over 10 years. It might be much, much more.

　　The next highest earner on the list is Serena Williams. Yet despite her having won six more slams, including all four between May 2002 and January 2003, the current Australian Open champion pulls in $7m less than Sharapova.

　　Why? 'It's not about the money to Maria, it's about winning, working hard and becoming a great champion,' says her agent Max Eisenbud. 'And this is what makes her so appealing to the world. She's on her way to becoming an icon.'

　　At some personal cost, it seems. In April, Sharapova celebrated her eighteenth birthday at New York's Hiro Ballroom. It was a bash organised by one of her sponsors and one wonders how many of her friends attended. Sharapova, who becomes animated when discussing her own brand of perfume, readily describes herself as 'part athlete, part businesswoman' - a rare explicit acknowledgement by a sports star that their corporate brand is as important as the game that made them.

　　Refreshingly honest, but where does that leave her tennis? 'Well, I know the balance between tennis and my off-court stuff so I've been able to deal with it really well. I enjoy everything that I do. If I felt I was doing too much then I wouldn't be doing it.'

　　Not everyone agrees, though. Following a 6-0 6-0 walloping by Davenport in the semi-finals at Indian Wells in March, Sharapova's coach Robert Lansdorp said: 'She's not physically strong enough to maintain the schedule that's been set for her.'

　　Sharapova mentions in Birmingham that she is tired, so I ask her if that's normal at this stage of the season. 'Are you trying to tell me I'm burnt-out or something?' she responds quickly. 'Because that's what it sounds like.'

　　I assure her, no, but wonder whether it is a concern going into Wimbledon. 'That's the life of an athlete. Every day you're going to wake up and not be feeling great. You might have a cold, but we travel around every single week so it's normal. There's so much bacteria around the world. If I was home every day I'm sure I wouldn't be sick. You have to find a way. I was really ill at the beginning of the year in Paris. I couldn't even walk.'

　　Sharapova pulled out of the Paris Open in February with flu, then continued with a schedule that has taken her to Hong Kong, Australia, Japan, the Middle East, Europe and numerous returns to Florida, where she lives. She has played 42 matches this year (36 wins, six defeats) and shown remarkable resilience. Following the loss to Davenport, Sharapova underlined her mental strength by reaching the final in Miami the following week, beating Justine Hénin-Hardenne along the way.

　　Sharapova and her father, Yuri, famously arrived at Nick Bollettieri's tennis academy in Florida with just $700 and no English. She was nine years old and would not see her mother, Yelena, for two years - she stayed behind in Sochi on the Black Sea. 'I speak to her a few times every day.

　　We are very close.' It must be a strain to Sharapova that her painfully shy mother does not follow her daughter on the circuit. 'The tougher the situation, the tougher you have to be mentally,' Sharapova says. 'I've always been tough. Since I was young I was expected to do well and people always thought I'd do great.'

　　Sharapova now travels with his daughter and, like Richard Williams, the father of Serena and Venus, and many more before him, he has a reputation for occasionally being overbearing.

　　'He [Yuri] was just yelling and screaming instructions. I thought he might just jump on the court,' said the 2004 French Open champion Anastasia Myskina after losing to Sharapova in the WTA Championship last November. 'If she joins our [Russia] team next season, you won't see me there.'

　　Sharapova is yet to represent her homeland in the Fed Cup, citing age, schedule and physical development as factors. 'We understand,' says Aleksei Selivanenko, vice-president of the Russian Tennis Federation. And Yuri's outburst in Los Angeles? 'He should not have done it. But life is long. The aim of the federation is to unite players and this is what we're doing. And everybody around them is welcome. It is like a soccer team - people may not like each other but they must play together.'

　　Having lived in Florida for most of her life, does Sharapova consider herself Russian? 'Of course.' Will you play for Russia? 'Yeah, of course I will play. I'm playing right now for Russia.' And the problems with the other Russian players? 'I get along with all of them. Right now I'm not ready physically to play Fed Cup, but I want to play it in future years for sure.'

　　Sharapova's victory over Hénin-Hardenne in Miami was her sole success against the Belgian this year and she lost to her in the French Open earlier this month. Does she regard Hénin-Hardenne as her main rival at Wimbledon? 'At the French I'm not going to say she was the better player.

　　Mentally she was stronger and looking back at the tape I was totally out of it. I didn't fight at all.'

　　Why? 'How I can tell you a month after that? I thought I did fight, but look at my face when it's three-all and look at hers. That's the difference.' But you would expect to beat her on grass? 'I'm going to do my best to beat everyone, not just her. Every match is different. We had a tough one in Miami and I ended up winning that, though she still played great tennis.'

　　Other threats over the next fortnight include Davenport and the Williams sisters. All three have won Wimbledon, though Serena has only recently recovered from the ankle injury that prevented her playing in the French Open and Venus, ranked 16, is a fading force.

　　Since last year, Sharapova believes, she has learned how to win from difficult positions, but she is still trying to improve 'all and every shot', and wants to play at the net more.

　　Now she is impatient to start playing in the tournament she describes as 'a homecoming'. Would she choose another Wimbledon title ahead of the other majors? 'Definitely. But it's going to be tough as I'm one of the ones to beat. But I won it last year and I can cherish that for the rest of my life.'

　　To keep the money coming in and those blue-chip sponsors happy Sharapova will have to keep winning the big tournaments. Whether she has the talent to win trophies and satisfy all those off-court commitments should be clearer by the end of Wimbledon fortnight.