Valentino Rossi's rivals face a battle to keep up with the MotoGP world champion on the track and an impossible task to match him off it going into Sunday's season-opening race in Qatar.

The Italian already has the pretenders to his throne under pressure before a competitive lap has been run after clocking the fastest times in two of the three pre-season tests on his Yamaha.

"The pre-season has gone well for me," Rossi, who won his ninth world title last season and his seventh in the premium class, told reporters ahead of the floodlit night race in the desert near Doha.

"Yamaha and (tyre-makers) Bridgestone have done a great job and we have been fast. We have only had six days on track so we still have work to do and things to learn about the new bike, but we are starting in good shape."

This year's entry list looks one of the strongest ever, with 13 of the 17 riders having won a World championship at some level in grand prix racing or superbikes while 16 of them are race winners.

A main challenger is expected to be Australia's Ducati riding 2007 world champion Casey Stoner, who has recovered from the health problems that disrupted him last season and is looking strong again.

Stoner has won the last three races in Qatar, including the two held at night, and was dominant from pole to flag last year.

Rossi's Yamaha team mate Jorge Lorenzo, last year's runner-up, is likely to be another, although the Spaniard is still not 100 per cent fit after injuring his hand in a motorcross training accident.

"Obviously Valentino will be in the battle, and then I think Stoner will be too," Carmelo Ezpeleta, the head of commercial rights holders Dorna, told Reuters.

"Maybe with Lorenzo it depends on how he recovers from his injury," said Ezpeleta, adding that Dani Pedrosa's chances of making a title bid depended greatly on Honda's ability to give him a competitive bike.

But while softly spoken Stoner and baby-faced Lorenzo might be able to give Rossi a run for his money on a bike, there is no contest when it comes to charisma and popular appeal.

Rossi, who has nicknamed himself the 'doctor', has become MotoGP's best ambassador thanks to his friendly, fun-loving disposition, his love of pranks and joke helmets as much as his remarkable sporting feats.

Italy's best paid sports personality is especially adored in his homeland, where he quickly repaired the damage caused by tax dispute by paying a 35-million euro bill to the Italian inland revenue in 2007.

This pulling power among fans and sponsors is a big part of the reason Ferrari tried to lure him away to Formula One in the past.

But motorcycling lovers hope Rossi, who has won 103 Grands Prix, will stay in the sport long enough to beat his compatriot Giacomo Agostini's record of 122 race wins.

"He is very important, not just commercially," said Ezpeleta. "Valentino is really one of our legends.

"He has been deeply involved in the MotoGP family and not just because he is a fantastic racer. He is involved in safety and many things like that. He really is very important."

Italian Loris Capirossi, at 37 the oldest racer on the grid, will be making an unprecedented 300th Grand Prix start on Sunday.

The former 125cc and 250cc world champion, now riding for Suzuki in his 21st season of Grand Prix racing, has held the record for the most starts since 2008 when he overtook Brazilian Alex Barros's mark of 276.

"I never thought I would get to this many but I have been lucky in my career and I have always given 100 percent and kept myself fit so that I have been able to stay at the top," the 37-year-old said in a team preview.

"I never really think about how many races I have been in but this number is very special and I guess it will probably never happen for another rider."