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.
MotoGP world champion Marc Marquez took pole position at the Grand Prix of the Americas with seconds to spare on Saturday after clambering over a wall and sprinting down pitlane to jump on his spare Honda.