The American suffered brain damage and other injuries - including fractures - after he was hit by a auto while out cycling with friends in Italy on Wednesday.
Hayden, 35, was hit by a auto while riding a bicycle near the beach town of Riccione on Wednesday, three days after racing in Italy's Imola track for the Superbike World Championship. "The prognosis remains reserved".
The Bufalini Hospital in Cesena said in a statement on Thursday: "Nicky Hayden's clinical condition remains extremely critical". The 2006 Champion has since been moved to Cesena hospital.
The "Kentucky Kid" won the MotoGP World Championship in 2006 and was competing in the World Superbike championship this year.More news: Always Dreaming a 4-5 favourite entering Preakness
Another channel said hat he has been placed under the medically induced coma.
United States Honda rider Nicky Hayden celebrates after winning the world Moto GP championship at the Cheste racetrack near Valencia, Spain. Paramedics stabilized him on site, and then he was taken to the nearest hospital with the highest gravity code. He was rushed to the hospital, and a recent update from his team confirms he is in "extremely critical" condition.
"We would like to thank everyone for their kind wishes and messages of support and the assistance of emergency and medical services". Once an official statement regarding Nicky's condition is released by the hospital or Nicky's family, a further update from the team will be issued.
"Nicky is one of the best friends I've ever had in the paddock", nine-time world champion Valentino Rossi wrote on his Instagram page.More news: Rex's Railroad Spike Teeth Were a Pulverizing Machine
"The most attractive moment I have about Nicky is when he shakes my hand after an unpleasant race at Valencia 2015".
Rossi added: "For him it was his farewell to MotoGP, I had just lost the world (title)". [The] supporting look inside his helmet is one of the few positive memories I have of that day.
"Forza Nicky, we're all with you".
Below are tweets from his former teammate Casey Stoner, reigning world champion Marc Marquez, Ducati rider Jorge Lorenzo and others praying for the American rider's quick recovery.More news: India confirm Champions Trophy participation
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