2006 MotoGP world champion Nicky Hayden has died days after being hit by a car in Italy.
Tributes are flowing for former MotoGP champion Nicky Hayden, who has died five days after being hit by a car.
"Thankful for the time that I was privileged to know you! Pray for his family during this time. We'll miss you mate!" Australian former MotoGP champion Casey Stoner said on Twitter.
Motorsport figures Lewis Hamilton, Dani Pedrosa, Marc Marquez, Felipe Massa, Sebastian Vettel, Jenson Button and Cal Crutchlow are among those to also express condolences.
"A beautiful person, genuine and real. RIP mate," retired Australian Formula One driver Mark Webber tweeted.
Hayden, nicknamed "the Kentucky kid", died aged 35 after suffering severe cerebral damage and multiple traumatic injuries in the incident in Cesena in northern Italy.
He was riding his bicycle at the time and was subsequently transported to Bufalini hospital on the Rimini coast last Wednesday.
Hayden was in Italy following a race at nearby Imola.
"The medical team has verified the death of the patient Nicholas Patrick Hayden, who has been undergoing care since last Wednesday May 17 in the intensive care unit of the Bufalini Hospital in Cesena following a very serious polytrauma which occurred the same day," the hospital statement said.
The black car that hit Hayden had its front windshield smashed.
Judicial authorities have opened an investigation into the incident and questioned the 30-year-old driver of the Peugeot.
Hayden won the MotoGP title in 2006, finishing narrowly ahead of Italian great Valentino Rossi.
In a MotoGP career spanning 2003-16 with Honda and Ducati, Hayden posted three victories and 28 podium finishes in 218 races.
After switching to the World Superbike championship last year, Hayden finished fifth in the 2016 standings.
Hayden was 13th in Superbike this season, riding for the Red Bull Honda team.
He was born in Owensboro, Kentucky.
Several family members had flown in from the United States, including Hayden's mother and brother.