Casey Stoner fears Yamaha and Ducati will be tougher opponents in MotoGP 2012

The world champion, who was speaking at the launch of Honda's RCV 213V in Kuala Lumpur, dominated last year's title race, winning 10 times and scoring 90 points more than his closest rival, Yamaha's Jorge Lorenzo.

However, with sweeping rule changes having come into play over the winter, including an increase in engine capacity from 800 to 1000cc, Stoner said that he will need to be on top form to fend off the threat posed by the likes of Lorenzo and Ducati's lead rider Valentino Rossi.

"We know there will be a lot of serious competition out there," said the 26-year-old Australian. "Ducati have been putting a lot of effort in as have Yamaha so it will be interesting to get out on track and see what everyone's got.

"I am sure Honda have done a fantastic job with the new 1000cc machine over the winter break and I'm really looking forward to getting back on the bike and seeing what we can do, hoping to start strong again.

Pre-season testing gets underway at Sepang on Tuesday, with both Stoner and his team-mate Dani Pedrosa set to ride.

Shuhei Nakamoto, Honda Racing Corporation's executive vice-president, said that testing restrictions meant that few changes could be made to the RCV 213V since its last major test at Valencia last November.

He confirmed that both Stoner and Pedrosa would have two chassis each at Sepang with which to undertake back-to-back runs during the three days.

"The machines we have brought here to Sepang are basically the same machines we tested in Valencia back in November with only a few differences," he said.

"In fact, Casey and Dani will have one machine the same as Valencia, and the other one with a slightly different chassis, based on their own requests."