Doohan: Rossi will be the greatest.

Former five times 500cc World Champion Mick Doohan believes that current MotoGP World Champion Valentino Rossi, who recently matched Doohan's premier-class title achievements, will now go on to become the greatest ever.

The two records that count most in motorcycle grand prix racing are premier-class wins and premier-class world titles.

On that count, Rossi's fifth crown puts him behind only countryman Giacomo Agostini - who clinched eight 500cc championships (seven consecutively) between 1966 and 1975 - while his 52 premier-class wins place him just two from Doohan and within 14 of Agostini's all-time record of 68.

With Rossi confirmed as staying in MotoGP until the end of next season - and with no sign of his current domination ending - it would be theoretically possible for the 26-year-old to beat Agostini's win record (and claim his sixth consecutive world title) by the end of next year.

However, even if that is achieved, Doohan believes Rossi will still stay on and beat Agostini's title haul.

"(Rossi's) got 10 years ahead of him - he'll not only surpass my achievements but anyone else's as well," Doohan told AAP. "Results-wise he's already equalled everything I've done and he'll have surpassed that by the end of the year, and that just leaves Agostini."

But Doohan doesn't agree with those that say Rossi's awesome domination, first with Honda and now Yamaha, is bad for the sport.

"You're watching the best of an era - if you want to watch second-rate people, go watch something else," Doohan said. "Rossi's hard to bet against - he's probably an odds-on favourite. The others can beat him (but) whether they will or not is a different story."

Doohan, who claimed all his titles with Honda, also disagreed with the current rumours about Rossi leaving the sport for Formula One or the World Rallying Championship.

"If he felt that's what he wants to do, then good luck to him - but I've always thought it was a bit of a media beat-up," said Mick.

Meanwhile, Rossi - who has won a total of seven world titles, when counting his 125 and 250cc crowns - now needs to win two of the remaining three races to break Doohan's all time season win record of 12, set in 1997.