American Ryan Newman is in a "serious but not life threatening" condition in hospital after crashing on the last lap of the Daytona 500 in Florida.
The 42-year-old was leading when his car was tapped from behind and it spun into the wall before flipping and being struck by another car.
US president Donald Trump gave the starting command on Sunday but the race was postponed until Monday due to rain.
"Praying for Ryan Newman, a great and brave Nascar driver," Trump tweeted.
The Daytona 500 is the biggest race of the National Association for Stock Car Auto Racing (Nascar) season.
Newman's Ford Mustang was tapped by Ryan Blaney, who was then beaten by Denny Hamlin in a photo-finish.
Newman, who won the event on 2008, was taken to a local hospital and an update on his condition was issued nearly two hours after the crash.
The statement read: "He is in serious condition, but doctors have indicated his injuries are not life threatening.
"We appreciate your thoughts and prayers and ask that you respect the privacy of Ryan and his family during this time."
The Daytona 500 runs for 500 miles (200 laps) but the 62nd edition of the race was extended to 522.5 miles (209 laps) due to an overtime finish.
Hamlin beat Blaney by 0.014 seconds - the second smallest margin of victory in the event's history.
It was a third win in five years for Hamlin, 39, who becomes just the sixth driver to win the race at least three times and the first since Sterling Marlin (1994, 1995) to claim back-to-back wins.