There is a scene that says more about Rafael Nadal than 1,000 documentaries. It is Paris, four years ago almost to the day. He has just won the French Open for the first time and is walking down the street; Uncle Toni, his coach, is on one side, and former professional player Carlos Costa on the other. Toni whispers to his nephew that he should afford Costa the respect and status he deserves by walking on the outside. The newly crowned champion obliges and quickly swaps places, and the three of them carry on into the night.

Today, Nadal has 30 titles and 6 grand slams to his name, including Wimbledon, and has banked around £17 million in winnings, with total earnings estimated at nearly £50 million. Despite that, those around him insist nothing has changed; the only difference being he wouldn’t need to be told to walk on the outside, he would already be there.

Arguably it is this surprising humility, conspicuous by its absence in so many sporting megastars, that has kept the tennis critics’ faith in Nadal even after he crashed out of the French Open this year. “It was a shocking, unprecedented, utterly unforeseen defeat,” says Times Tennis Correspondent Neil Harman. “But in the press conference afterwards, Nadal proved his mental strength, calmly pointing out how one needs defeat to give value to your victories. He still has three or four years until he reaches his peak, but already he is in the top five tennis players of all time.”

In fact, it is a measure of Nadal’s dominance that his defeat sent such massive reverberations through the sport. After all, up until then, he had been busy rewriting the tennis record books. Last year, he finally topped the rankings after 160 weeks at number two, and won the Davis Cup for Spain, gold at the Beijing Olympics and seven other titles. This year he has gone on to win in both Monte Carlo and Barcelona for a fifth successive time, as well as the Italian Open for a fourth time, all at 22 (he’s just had his 23rd birthday). But, while his trophy cabinet and number of screaming fans have swelled proportionately, life for the boy from Majorca remains very much the same.

He still lives at home with his mother, father and sister at their flat in Manacor, still carries his own bags, looks after his own kit (his mother washes and irons his clothes), hangs out with his old friends, dates a local girl, 21-year-old Francisca “Xisca” Perello, goes fishing with friends in a boat out of Porto Cristo harbour, and still has the threat from his Uncle Toni that, if he starts acting up, he can look for a new coach or find a new sport.

“He told me when I was very young that if I ever started throwing my rackets around, smashing them or hitting balls out of the park, then he would send me out of the park,” recalls Nadal. “He used to say that there were many children and grown-ups who have never had the chance to play, so a racket should be loved. I have never thrown a racket in my life. It taught me that it doesn’t matter how badly you are playing, it is not the racket’s fault; you should always show respect.”

We are sitting in his hotel room in Rome – perhaps the only thing that has changed is the fact that he resides in a suite rather than a standard room – which, in spite of its abundant luxury and the fact that he has spent less than an hour there, is already more than halfway towards looking like a student bedroom. A few photos Blu-Tacked to the walls and the makeover would be complete.

Clothes are strewn around, trainers and socks form footsteps on the carpet as though discarded as he walked across the room. Half-unpacked cases spill their contents across the floor; two young Spaniards are lolling on the sofa playing a computer game; the television is on; someone is chatting on their mobile; and in the middle is Nadal, dropping his jeans, tucking in his T-shirt and hitching himself up. Only his rackets seem ordered, resting neatly in their bag by the door. It is a scene utterly devoid of affectation or self-importance.

Yet it is this man, with a physique that appears to have been hewn from granite and an almost terrifying determination, who last year usurped Roger Federer to become No 1 in the world. He would have been defending his title at the AEGON Championships at the Queen’s Club, London, this week, were it not for a knee injury. “The doctors said I should rest if I want to be ready for Wimbledon. I watched my Wimbledon final from last year on TV recently. It was amazing, so amazing, and I am determined to be there again.” He identifies the principal threat to his Wimbledon crown as Britain’s Andy Murray. Murray’s own position in the rankings has gone from outside the Top 10 to No 3 in the past year. It is a mouth-watering prospect, and possibly the opening salvo of what may be a long-term rivalry. On one side of the net, there is the brutal power and never-say-die intensity of the Spaniard; on the other, the silkier, more diverse shot-making of the less demonstrative but equally determined Scot. It is a fascinating contrast in style and temperament, yet away from tennis, both seem almost untouched by their success.

“Why would I want to change anything, why should I change anything?” Nadal asks, rather disarmingly. “The atmosphere in my home is lovely. Why would I want to get somewhere of my own, and then come back to an empty apartment, and worry about whether I had any food left in the fridge and things like that? It’s much nicer to come home to my family, where everything is as it always was, my mother telling me to tidy my room, my sister, Maria Isabel, teasing me. Stability is very important to me.”

Nadal may have traded in his battered old mobile phone, but his car is not luxurious or ostentatious, just a Kia – something practical to get him around the island with his golf clubs. And he hasn’t bought his own boat to go fishing, preferring his father’s instead.

“Of course, it’s good to have money, and it’s a privilege to be in a situation where I don’t have to worry about it, but that’s not the reason why I play tennis and it’s not a motivation. I had a wonderfully happy childhood and I am just as happy today, so I know that money doesn’t change anything or bring additional happiness. I play because I love it. For me, the most important thing is practising, trying to get better and improve every aspect of my game. I assume nothing.”