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The Italian, who moves from the works Honda squad to Tech 3 Yamaha for 2012, tweeted a picture of his injury late on Thursday night, commenting: "I broke my right collarbone doing motocross."

Hayden meanwhile broke his left scapula and fractured two ribs in a training accident in Kentucky at the end of December.

Dovizioso's new team is yet to comment on the implications of his injury, but with MotoGP's first test of the year commencing at Sepang, Malaysia, on 31 January, both he and Hayden face a battle to be fit in time to participate.

Dovizioso, 25, finished third in last year's MotoGP championship, having taken seven podiums over the course of the season.

Despite that he was released from his works deal with Honda, the Japanese manufacturer opting to run just two riders in the works team due to budget constraints.

He signed for Tech 3 Yamaha, where he will partner Cal Crutchlow for the 2012 season.

Both Crutchlow and his 2011 team-mate Colin Edwards broke their collarbones during MotoGP events last year.

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