Motorcycling world champion Valentino Rossi has said a switch to more powerful engines in 2012 could persuade him to stay in MotoGP.

The Italian added in an interview conducted by his Yamaha team ahead of the first test of the season in Malaysia that he was unlikely to switch to Formula One, despite recently testing again for Ferrari.

"Theoretically I am very happy to go back to the 1,000cc (bikes) because I like it more than 800cc and it is more fun," the 30-year-old said of the proposed rule change for the top category.

"Of course we will have to see how the technical regulation will be for these engines and we will have to see whether they are fast and fun to ride like they were in 2006.

"Anyway, going back to 1,000cc is an important challenge, as far as my motivation is concerned, and may convince me to stay in MotoGP for longer."

The Italian was less happy about rule changes for 2010 which restrict riders to six engines per season as a cost-cutting measure similar to those introduced in Formula One.

"I think it will be a difficult rule for everybody because just six engines for one season are not enough, it is very tight. If we have eight or 10 it is easier and less risky," he said.

Rossi tested a Ferrari Formula One car in Spain last month for the sixth time, setting impressive times. The nine times world champion has a contract with Yamaha until the end of this year and has talked about an eventual switch to cars, probably in rallying.

"I did another test with the Ferrari F1 car in Barcelona, it was great," said Rossi. "I had fun and it was a very good test, with good lap times, but I think it will be very difficult to see me in Formula One."

The Italian said he would have a clearer picture about his future later this year.

"I am very good at Yamaha so I will talk to them first," he added. "Then we will see."