World champion Valentino Rossi, whose campaign has been wrecked by a four-race, injury-enforced absence, chases a third successive San Marino Grand Prix victory on Sunday.

The 31-year-old has been forced to write off his title hopes and stands a huge 137 points behind Yamaha teammate Jorge Lorenzo ahead of his home race, but is only five points behind Australia's Casey Stoner in fourth place in the standings.

Stoner is being replaced by Rossi at Ducati next season while the Australian leaves for Honda.

"This is my home Grand Prix because I live just 10km away and I have spent a lot of time on this track, starting with the Italian Sport Production bikes," explained 31-year-old Rossi.

"I've had two fantastic races here the last two years, so there are a lot of expectations from the fans ahead of this weekend. This race will be hard on the body with all the hard braking, but we must try very hard to make a good result."

While Rossi has his future sewn up, Lorenzo, who has won eight of 11 races this season, is still waiting to put pen to paper on a new Yamaha agreement, but the Spaniard is not concerned about his situation.

"I hope to have everything sorted for the 2011 season in the next few weeks," said 23-year-old Lorenzo, who still has a 68-point lead in the title race despite Honda rider Dani Pedrosa's win in Indianapolis last weekend.

Lorenzo admitted he had been unfit in the US although he still did enough to secure third place for a 11th podium place of the campaign.

"I had a lot of problems with my physical condition. Even on the Monday I didn't feel completely fit, but I'm sure I'll be back to full fitness ready for Friday," he said.

Pedrosa's victory in Indianapolis was his second of the season and the Spaniard believes it is crucial to maintain his form until the end of the season.

"It would be great to carry on this weekend where we left off at Indianapolis, but we know this is a hard track for us, so we need to work hard from Friday onwards," said Pedrosa.