Hayden was 35.
Last week, the Bufalini hospital in Cesena announced Hayden had severe cerebral damage and multiple traumatic injuries.
“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.
Hayden, who was in Italy following a race at nearby Imola, was transported to the Bufalini facility following the incident on the Rimini coast on Wednesday.
The black Peugeot 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.
Hayden was born in Owensboro, Kentucky.
Several family members had flown in from the United States, including Hayden’s mother and brother.
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