Four-time IndyCar champion Dario Franchitti has fractured his spine and broken his right ankle in a high-speed crash at the Houston Grand Prix.
The Scot, 40, suffered multiple fractures after hitting the track wall.
His car flipped into the air following a final-lap collision with Takuma Sato, with at least 13 spectators injured by debris that flew over safety fencing.
Franchitti's team owner Chip Ganassi said: "His ankle and back are a little sore. He is going to be okay."
Three-time Indianapolis 500 winner Franchitti hit the back of Sato's car and was propelled into the air and against the fence. His car exploded into several pieces but did not catch fire.
Sato said his car "caught the marbles", chunks of rubber that come off the tyres and lie on the track, before brushing the wall and losing momentum.
"A couple of cars passed me as I was offline and in turn five," said the Japanese driver. "I got very loose and Dario and I came together."
IndyCar later released a statement confirming Franchitti was awake on his arrival at the hospital and would be monitored overnight
The statement read: "IZOD IndyCar Series driver Dario Franchitti was admitted awake and alert to Memorial Hermann Texas Medical Center in Houston for a concussion, spinal fracture that will require no surgery and a fracture to the right ankle. He will be kept overnight."
Actress Ashley Judd, who married Franchitti in 2001, though the pair separated earlier this year, tweeted that she was on her way to Houston to see him.
Race promoters said 11 spectators were treated at the track while two more were transferred to hospital for evaluation.
Franchitti's former team-mate Dan Wheldon, from England, died in a crash at the Las Vegas Indy 300 in October 2011.
Will Power, who won the Grand Prix, said the accident reminded him of the Las Vegas crash, where he and Wheldon both hit the fence.
"Yes, that's what it reminded me of," he said. "I just saw Dario's car and him sitting in it with a lot of damage. I hate seeing that. We try to keep these cars on the ground."
Franchitti's team-mate Scott Dixon, who leads the overall standings, echoed Power's thoughts.
"The smells and the visuals, you have the remnants of Vegas popping into your head, with you coming around the corner and you can't drive through it because there's a field of debris," he said.
"There was nowhere near the amount of damage that we saw (in 2011), but seeing the replay was a big shock."