[Acidreign]

By Julien Pretot -- PARIS, May 18 (Reuters) - World champion Valentino Rossi says the next few races, starting with Sunday's French Grand Prix, will be critical to his hopes of winning a sixthsuccessive title.

The charismatic Italian retired from the last race in China with a tyre failure and returns to Europe lying sixth in the standings, 32 points adrift of Honda's American pacesetter Nicky Hayden.

"We lost ground in the championship and I'm very disappointed with that but there are still a lot of races remaining until the end of the season," said the 27-year old
Yamaha rider.

"Luck has definitely not been on our side but the most important thing now is to sort our problems out as soon as possible because we have a run of important races coming up --
starting at Le Mans.

"The next four or five rounds in Europe are the 'main course' of the season and it is a critical time for us."

Le Mans is not a favourite track for Rossi, although he won there from pole position last year and set the fastest lap in the process, and he arrives this time struggling with a
troublesome bike.

While Rossi has been pleading with Yamaha to sort out the problems, Hayden will be more determined than ever to take his first win of the season after eight podium finishes in a row.

"While getting the points and podiums is very good, I really want to win. I like to think that the win is not far away," said Hayden.

He will have to hold off the challenge of Spanish team mate Dani Pedrosa, the 20-year-old who celebrated his first win in Shanghai in only his fourth race in the MotoGP category and is brimming with confidence.

Pedrosa is 15 points behind Hayden and just two adrift of second-placed Italian Loris Capirossi, the early leader in the title race after winning in Spain.

The Ducati rider finished eighth in China and remained optimistic: "We must keep working hard. I know I can win, so when the moment comes...I will be up front," he said.

The French track, which also hosts the 24-Hour Le Mans series, is a very tight circuit with a lot of first gear corners and hard accelerations.

Local favourite Randy De Puniet will make his home MotoGP debut on a Kawasaki after scoring points in the last two rounds. Last year, he took both pole position and the lap record in the lower 250cc category.

Italian Andrea Dovizioso is eager to extend his three-point lead in the 250cc standings with a first win this season but will be under pressure from Spaniard Hector Barbera, a winner in China for Aprilia.

After four races and two wins, Spain's Alvaro Bautista looks comfortable in the 125cc category with a 28-point lead.

((Editing by Alan Baldwin, London Sports Desk; Reuters messaging: julien.pretot.reuters.com@reuters.net; +33 1 4949 5370))