Tony Stewart hits wall in 3-car wreck at Dover

Tony Stewart smacked into the wall during Friday's practice run at Dover International Speedway in an accident that also involved Danica Patrick and Jamie McMurray.

Stewart, who recently recovered from a broken back, gingerly climbed out his vehicle and was examined at the medical center in the infield of the track.

Patrick and McMurray also hit the wall and were also examined at the medical center. McMurray suffered a left elbow injury.

The wreck was apparently caused by a gear failure in Patrick's Chevrolet and it sent oil across the frontstretch of the track. The cars of Stewart and McMurray both slid in the oil and slammed into the outside wall at high speeds.

All three cars were heavily damaged and Patrick's Chevrolet caught on fire.

"I don't know if it was human error or bad luck," Patrick told reporters. "I hit the wall. Obviously, there was some kind of oil or something that created that. It's not something we commonly see."

Patrick was concerned about the condition of Stewart, her Stewart-Haas Racing teammate who has announced that he is retiring after the season.

"I think at any point you worry about Tony," Patrick said. "Hopefully, he's all right."

Stewart -- as well as Patrick and McMurray -- were using backup cars when practiced resumed.

Friday's practice was the first for Sunday's AAA 400 Drive for Autism Sprint Cup race.