Jeff Gordon was forced to miss most of Saturday's NASCAR Sprint Cup practice at Charlotte due to back spasms.
Gordon completed just 11 laps before telling the Hendrick team that he was unable to continue driving.
"It's unfortunate," Gordon said. "I've had some spasms in the past, but this one's a little bit different.
"I just want to be cautious and take care of it. It doesn't do me any good to be in the car right now, especially with the car as good as it is.
"It's all about being ready for 600 miles tomorrow."
The three-time Charlotte 600 winner, who ended the day with the sixth-fastest practice time, underwent surgery in 2009 to relieve back pain.
Hendrick Motorsports has Regan Smith on standby to take over its #24 car for the race if Gordon is unable to compete.
Smith is one of two standby drivers already on hand, with Parker Kligerman lined up by Stewart-Haas should Kurt Busch suffer any delays travelling to Charlotte from the Indianapolis 500.