The Swiss rider Jason Dupasquier, who had a serious accident at the motorcycle world championship in Italy, died on Sunday.
This was confirmed by a spokesman for the Careggi Hospital in Florence of the German press agency.
The 19-year-old fell in a curve during the Moto3 qualifying race at the Mugello Motodrom on Saturday.
At least one subsequent driver should have touched or even rolled over him.
However, the TV images cannot explain the course of the accident.
Dupasquier had had an operation on his chest on Sunday night.
However, he had also suffered severe brain damage.
"On behalf of the entire MotoGP, we send our love to his team and his family," the message said: "We will miss you very much." a few minutes after the death was announced.