Media reports said the "Kentucky Kid", who won the MotoGP championship on a Honda in 2006, is in a serious condition.
Former MotoGP champion Nicky Hayden spent a second day in intensive care on Thursday after colliding with a car while cycling in eastern Italy.
Former MotoGP champion Nicky Hayden died five days after the American was hit by a car while cycling in eastern Italy, his Honda World Superbike team said.
Honda's former world champion Nicky Hayden set the pace on the final day of MotoGP's official pre-season test at the Jerez circuit in southern Spain on Monday. The American, who lost his crown to Ducati's Australian Casey Stoner last season, clocked the fastest time of the test with a lap of one minute 38.848 seconds at the end of the afternoon.
Honda's Toni Elias stormed from behind title contender Valentino Rossi to win the MotoGP Portuguese Grand Prix on the final lap on Sunday.
Ducati's Loris Capirossi stormed to victory in the Japanese Grand Prix, with champion Valentino Rossi finishing second.
Italian Loris Capirossi won the MotoGP Czech Grand Prix after leading from start to finish.
American Nicky Hayden boosted his MotoGP championship hopes with a second straight US Grand Prix victory.
While Valentino Rossi's bid for a sixth 500cc crown suffered a punishing blow.
The Italian kept alive the defence of his MotoGP title with a battling victory in the German Grand Prix.
Former world champion Valentino Rossi won the MotoGP at the Dutch Grand Prix after a 15 lap battle with overall leader Casey Stoner on Saturday.
The Italian Yamaha rider fought from 11th position at the start for his second straight win at the twisting Sachsenring circuit.
Italian Valentino Rossi extended his contract with Yamaha to the end of 2008.
Yamaha's Colin Edwards, overtaken by his Honda rival on the penultimate lap, seized back the lead but then crashed at the final chicane.
The American ended world champion Valentino Rossi's run of five consecutive MotoGP wins with victory in the US Grand Prix.
American Nicky Hayden finished third in Valencia to claim his first MotoGP world title.
Valentino Rossi made it five MotoGP wins in a row at the Italian Grand Prix
Yamaha's Jorge Lorenzo trimmed the gap to championship leader Dani Pedrosa at the top of the MotoGP standings to seven points when he stormed to victory at a sweltering Catalunya Grand Prix on Sunday.