Justin Wilson was airlifted out of Pocono Raceway and is in a coma after he was hit by a large piece of debris during Sunday's IndyCar race.
Wilson suffered a severe head injury and is in critical condition at Lehigh Valley Health Network Cedar Crest Hospital in Allentown, Pennsylvania, IndyCar announced. The series said he remains in a coma as of Monday afternoon.
Wilson was struck in the head by a piece of Sage Karam's car when Karam spun into the wall. Wilson's car veered left and directly into an interior wall.
He was swarmed by the safety crew and airlifted by helicopter from the track.
"It's just a tough one right now," said Michael Andretti, car owner for both Wilson and race winner Ryan Hunter-Reay. "Our thoughts and prayers are with Justin right now. We're going to see. Hopefully, he's OK."
In Victory Lane, Hunter-Reay said his thoughts were only with Wilson, an extremely popular driver in the paddock who speaks on behalf of his peers regarding safety and competition.
"All I know is that he was unconscious, he was not responding and he was airlifted," Hunter-Reay said. "That's all very bad. I'm very worried right now."
Stefan Wilson, Justin's brother, tweeted what little he knew about Justin Wilson's condition.
Justin Wilson's wife, Julia, was transported to Pennsylvania from their home in Colorado by IndyCar, while Stefan Wilson was traveling from Indianapolis. Tony Stewart loaned his plane and pilots to Stefan Wilson so he could get to his brother's side.
Hunter-Reay tried to get an update on Justin Wilson before the race resumed and again before he climbed from his race-winning Honda.
"Maybe in the future we can work toward something that resembles a canopy," Hunter-Reay said. "Something that can give us a little bit of protection and still keep the tradition of the sport. Just to be [an] innocent bystander like that and get hit in the head with a nose cone is a scary thought."
IndyCar driver James Hinchcliffe suffered a concussion in May 2014 when debris from an accident struck his helmet during the inaugural Grand Prix of Indianapolis on the Indianapolis Motor Speedway road course. The injury caused Hinchcliffe to miss several days of practice, but he was able to compete in the Indianapolis 500 two weeks later.
The 37-year-old Wilson, a native of Sheffield, England, entered this season without a full-time ride. He latched on with Andretti and was in the sixth of seven scheduled races with the team. The deal was put together right before the season-opening race in March and initially started as a two-race agreement at Indianapolis.
Sponsorship was found for another five races as the season progressed, and Wilson finished a season-best second earlier this month at Mid-Ohio.
He said after that race that he raced clean and did not take any risks that would have jeopardized eventual race winner Graham Rahal because Rahal was part of the championship race and Wilson was not.
Wilson broke a bone in his back at Mid-Ohio in 2011. He missed the final six races of the season and wore a back brace for more than two months as he was restricted from any physical activity.
Wilson said in 2012 that his injuries and the death of driver Dan Wheldon in a crash in 2011 did nothing to change his perspective or make him question his career choice.
"I've had the conversation with Julia -- this is what we do, and you try to make the best plans if that ever happens," Wilson told The Associated Press upon his return in 2012. "You've got to know the risks and work out if those risks are acceptable. To me, it's acceptable. But I'm not going to stop trying to improve it.
"All the drivers, this IndyCar, we're always trying to make it safer, but at the end of the day, it's a race car. We're racing hard, we're racing IndyCars and it's fast. When it goes wrong, it can get messy."
Wilson broke his pelvis and suffered a bruised lung in the 2013 season finale at Fontana.
"It's only natural that when there is a situation like this -- a dire situation -- that breeds innovation," Hunter-Reay said. "It's unfortunate that's the way life is in general. That's the way everything works. Hopefully, Justin is OK, and we can look at it in a positive light on that side of it and move forward on some kind of progress on that problem of debris flying through the air."
ESPN.com's John Oreovicz and Bob Pockrass and The Associated Press contributed to this report.