English driver Justin Wilson was airlifted to hospital with a head injury on Sunday after he was struck by debris from a late-race crash and hit the wall in the IndyCar race at Pocono.
IndyCar officials said that Wilson, 37, had suffered a head injury, but gave no further details.
The Andretti Autosport driver appeared to have been struck by a piece of debris from Sage Karam's car when it crashed in front of him during the final laps on the "Tricky Triangle" of Pocono Raceway.
Karam was leading when his Chip Ganassi Racing Chevrolet spun on lap 179 of the 200 lap race.
A piece of the car appeared to strike Wilson, whose car then swerved into a wall.
His Andretti team-mate Ryan Hunter-Reay won the race, which finished under a caution flag.
It's not the first time that a driver has been injured when hit in the head by debris in recent years.
James Hinchcliffe suffered a concussion when he was hit by flying parts at the 2014 Grand Prix of Indianapolis.
Wilson has driven in major US open-wheel racing since the 2004 season.
He was driving a partial schedule in 2015 for Andretti Autosport.
He has seven wins in CART and IndyCar races, his most recent coming at Texas in 2012.