Stewart hit the wall in turn three on his second lap during the first morning practice. His No.14 Chevrolet suffered significant damage to the right side, forcing his Stewart-Haas Racing team to switch to an alternate car for the Sunoco Red Cross Pennsylvania 500 on Sunday.

"I screwed up," Stewart said. "I got in too deep and got loose and couldn't save it."

Stewart, the current points leader, was awarded the pole at Pocono after rain forced cancellation of Friday's qualifying session.

In June, Stewart also had to relinquish his pole position and start from the back of the field for the Pocono 500 after wrecking in final practice. Qualifying was cancelled for that event due to inclement weather. Stewart gambled on fuel late in the race en route to his first victory as driver and owner.

Stewart's backup car for Sunday is the same one that gave him a eighth-place finish at California and a third-place run at Darlington earlier this year.

"I know we can do it," he said. "I tore up a really good race car today."