MotoGP world champion Valentino Rossi [ Images ] said he was moving to Italian team Ducati because his work with Yamaha was finished and they no longer needed him.

Rossi, one of Italy's [ Images ] most famous sports personalities, will race for Ducati next year on a two-year contract. He has been with Yamaha since 2004.

He told reporters on Monday at the Czech circuit in Brno, scene of Sunday's Grand Prix [ Images ]:

"I'm happy, I'm very curious and very motivated. This new challenge, I think, will be very interesting - especially because I think that at Yamaha my work is finished."

Rossi added: "We changed the situation from 2004 a lot. Yamaha have great riders so it looks like they don't need me any more."

Clear championship leader Jorge Lorenzo of Spain also rides for Yamaha.

A vacancy at Ducati arose after Australia's [ Images ] Casey Stoner said last month he would be leaving for Honda next year.

Looking forward to 2011, Rossi said: "I think an Italian rider on an Italian bike is great for all the Italian fans and I think we will have a lot of cheering from all the Italian fans."

Yamaha managing director Lin Jarvis added: "Unfortunately he's made finally the choice to go and ride for Ducati next year so it was a sad day yesterday because although we've known about his decision for some weeks nevertheless when you make the final public announcement it becomes a fact."