Reigning MotoGP champion Valentino Rossi has conceded his title defence could already be over.

The previously all-conquering Italian has been the champion of motorcycling's premier racing class since he first took the world crown in 2001.

But heading into this weekend's Czech Republic MotoGP, the Camel Yamaha rider lies fourth in the overall standings, trailing leader Nicky Hayden of Repsol Honda by 51 points.

American Hayden won last time out in the USA MotoGP at Laguna Seca while Rossi was left frustrated after a breakdown.

And ahead of today's opening practice sessions at the Automotodrom, Rossi, who is based in London's Mayfair, said: "We only have six races left, which is maybe not enough to make up the difference to Hayden.

"But anyway, I want to have some fun and win as many races as possible between now and the end of the year.

"Right now I'm not even thinking about the championship.

"I want to take it race by race and to find a better way forward with this bike and these tyres."

But the omens could be on Rossi's side as the weekend marks a decade since Rossi took his maiden GP win - at Brno - in the 125cc class.

And at the same circuit last year, Rossi set a fastest lap time as well as winning the race on the way to a fifth consecutive championship crown.

Camel Yamaha team manager Davide Brivio said: "Brno is the start of the final stage of the season and we go into it finding ourselves in a difficult situation.

"We're obviously not where we'd like to be in the championship with six races to go.

"But we will not give up and every member of the team is ready to fight until the end.

"Of course we still want to win the title and we still believe we can, so although we have had a lot of misfortune during the season we still have faith in our potential.

"The four-week break since Laguna Seca was good for everybody but now we're looking forward to getting back on the track and trying to win races again.

"That's Valentino's goal for every GP between now and the end of the season."

Meanwhile, Marlboro Ducati rider Loris Capirossi is hopeful of adding to his one and only victory of the season so far, which came in the opening race of the year in Spain.

And Capirossi said he expected tyre quality to play a decisive part over the weekend.

"Brno is very good for our tyres," said the 33-year-old. "And last year it was the place where we started a good run of results for us and for Bridgestone.

"You also need a well-balanced bike for Brno because some corners have positive camber and other have negative camber.

"You also need a strong engine because there are some big uphill straights."