The Swiss rider was on the sighting lap of Sunday afternoon’s Moto3 race when he was rear-ended at high speed by Jose Antonio Rueda.

Dettwiler was riding slowly on the racing line after apparently discovering an issue with his bike shortly after he left the pits.

With his head tucked into the front fairing, it appeared Rueda did not notice Dettwiler riding slowly.

Both riders were attended to by trackside marshals before being flown to a nearby hospital by helicopter.

Rueda suffered a fractured hand and bruising. Dettwiler, however, suffered serious injuries that required multiple surgeries.

“Noah has undergone several surgeries in the last few hours, which went well,” read a statement on behalf of CIP Green Power Team and the Dettwiler family.

“According to the doctors in charge, his condition is stable but still critical.

“We appreciate your understanding and ask that Noah and his family’s privacy be respected at this time.

“Thank you for all your incredible support and messages.”

Moto3 is the third division of grand prix motorcycle racing below MotoGP and Moto2.