Alex de Angelis has reportedly suffered "rib fractures as well as multiple spinal bone fractures" in a horrific crash at Motegi.
The San Marino rider was putting in the laps in final practice when he crashed heavily 10 minutes into the session.
The session was red-flagged as medics treated him before he was taken by helicopter to the Dokkyo Hospital in Mibu for further examination.
He was conscious and breathing before being airlifted.
The initial reports revealed that he had suffered a lung contusion while a CT scan has also diagnosed fractures.
MotoGP Tweeted: "CT scans on Alex de Angelis reveal rib fractures as well as multiple spinal bone fractures."
De Angelis, who races for E-Motion IodaRacing Team Aprilia, has scored two points to date this season having finished P15 in Catalunya and again in Britain.