In the past he has turned up to races wearing pink leather trousers and riding an Hawaiian bike, installing trackside palm trees and inflatable swimming pool for his fans, but Valentino Rossi was keeping an unusually low profile in the Czech Republic yesterday amid mounting questions about his performance both on and off the track.

Trailing Casey Stoner, Ducati’s 21-year-old upstart, by 44 points is one thing, but the pointed fingers and paddock gossip about tax evasion mean that Rossi has never been under such pressure. Italy’s tax agency has confirmed the Fiat Yamaha star is being investigated for possible tax evasion on €60 million (about £40 million) pocketed between 2000 and 2004. Loris Capirossi, Stoner’s teammate, has also been accused of not declaring €1.3 million on top of a previous €13 million.

However, it is Rossi’s case that has dominated the media in Italy, with one newspaper printing pictures of boats and cars allegedly bought in Italy while he was supposedly living in Mayfair. Yesterday, at the Brno circuit ahead of a race crucial to Rossi’s hopes of regaining his world crown, the flamboyant Italian was tight-lipped. He refused all interviews and insisted that he will go to the postrace press conference on the proviso that all questions are about motorcycling. In another twist, it is believed that Gibo Baldi, his long-term manager, has left his position.

Rossi has not been silent, however, and recorded a videotape that was delivered to RAI, the Italian broadcaster, in which he mounted a passionate defence. “I’ve been crucified and condemned even before any of the necessary checks have been carried out,” he said. “I have been living in London for seven years, not a Disney city or a tax paradise on a small island. The professionals who handle my income declarations have assured me that they respected the rules, as I have always asked them to do. This story will be over very soon.” Perhaps so, but the taxman cometh.

It is alleged that Rossi’s main business and financial interests remained in Italy, even after he told the media that he was living in London, thus making use of the tax loophole that allows nondomiciled residents to declare only income accrued in Britain. The taxman wants to know what happened to the lucrative sponsorship and bonuses that make Rossi Italy’s best-paid sportsman. Vincenzo Visco, deputy economic minister, has weighed into the scandal, saying: “I’m sorry for Rossi and I’m a huge fan of his, but the law has to be obeyed.”

Rossi has always maintained that he moved to London to get away from the glare of publicity at home. His management company, Great White, has a registered office at Sackville Street in London. “Today I’m the target of astronomical tax investigations and tomorrow, who knows, I could be a spaceman on Mars,” Rossi said.

It is a sideshow that he could do without. Last year he failed to win the MotoGP world title for the first time since his rookie season in 2000. This year he has found no answer to the power of Ducati and the brilliance of Stoner and his mask of invincibility has slipped. If he loses to the sport’s new wunderkind on Sunday, the times may be changing as well as taxing.

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