The 32-year-old, from London, was treated at the circuit before transferred to hospital by helicopter.
Japanese news agency Kyodo News reported that police described the English rider’s condition as “serious” and stated that no spectators or race officials were injured in the incident.
The former British Superbike rider was riding for the FCC TSR Honda France team in the eight-hour endurance race, which is scheduled to get under way at 03:30 BST.
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