An Italian crackdown on tax cheats has swept up former motorcycle champion Valentino Rossi, shocking a nation with the thought that a fresh-faced sports hero could be involved in evasion.

Rossi, whose seven world titles and marketable boy next door charm have helped make him Italy's richest sportsman, is being investigated for suspected tax evasion on undeclared revenues of 60 million euros ($A96.22 million), the state tax agency said.

Rossi said his tax consultants were checking the matter.

The inquiry is linked to his decision in 2000 to take up residence in Britain to take advantage of its tax regime.

"For seven months of the year I travel the world for my job. The tax agency is rightly doing its job ... my consultants are already examining the issue," he said in a statement late yesterday to the ANSA news agency.

The 28-year-old rider is the biggest name to be caught up in the fight against tax cheats since Italian agents seized Argentinian soccer legend Diego Maradona's Rolex watches last year to help pay off back taxes.

"There is a special sorrow ... in discovering that even a boy who is young, lucky, a genius in his field, the freshest and most unusual among personalities to have come out in recent years, is mixed up in the same old intolerable muck that makes this country unliveable," a la Repubblica columnist said in a front-page editorial.

"Rossi might be a phenomenal sportsman, but a naive taxpayer," Corriere della Sera wrote.

Italy has been riveted by the bubbly Rossi since his first world title 10 years ago.

The Yamaha rider is the youngest man to have won world titles in all three motorcycling classes. He won four MotoGP titles from 2002 to 2005.

He lost his title last year to American Nicky Hayden. Rossi is second in the 2007 standings behind Australia's Casey Stoner.

Italy's centre-left government estimates the cost of tax evasion at seven per cent of gross domestic product, or about 100 billion euros ($A160.36 billion) a year.

Italy could turn to the European Union to try to strike down British law under which "a more or less fictitious residence in London allows you not to pay taxes in your own country", said Vincenzo Visco, the government's tax chief.

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