British driver Justin Wilson sustained severe head injuries and is in a coma in a critical condition after he was struck by debris from another car during the closing laps of the penultimate IndyCar race in Pennsylvania.
The 37-year old former Formula One driver, a seven-times winner in IndyCar racing, was airlifted to hospital and will remain there for further evaluation, IndyCar officials added.
Wilson's car was apparently out of control after being hit by the debris and veered into the wall at the Pocono Raceway in Pennsylvania.
His Andretti Autosport team mate Ryan Hunter-Reay, who went on to win the 500-mile (804.67 km) race, said he had not heard of the Briton's condition in hospital though he had been unconscious at the track.
"All I know is that he was unconscious," Hunter-Reay said.
"He was not responding. He was airlifted. That's all obviously very bad details."
Wilson's crash was reminiscent of a 2009 incident when Brazil's Felipe Massa was struck in the helmet by a spring from Rubens Barichello's car during qualifying for the Hungarian Grand Prix and had to undergo surgery.
The New Zealander Scott Dixon finished ninth and remains third overall.