Back spasms sideline Jeff Gordon during practice

After winning the NASCAR Sprint Cup Series race May 10 at Kansas Speedway, Jeff Gordon said he felt 25 years old again.

On Saturday at Charlotte Motor Speedway—not so much.

Gordon, 42, suffered back spasms on his final qualifying run Thursday night at the 1.5-mile race track, and the lingering effects could jeopardize his participation in Sunday’s Coca-Cola 600.

NASCAR Nationwide Series title contender Regan Smith is standing by in case Gordon needs a relief driver for the sport’s longest race.

Gordon, who is celebrating the 20th anniversary of his first NASCAR Sprint Cup Series victory this weekend, ran 11 laps in Saturday morning’s first practice session before bringing his car to the garage and parking it for the rest of the day.

“Unfortunately, I had a back spasm the other night in the last qualifying run that I made,” Gordon said after exiting the No. 24 Chevrolet. “And I’ve been trying to get it worked out by today, and it just wasn’t.

“The good news is that the car is awesome. So I made 11 laps, and it was everything I could do to do that. I just had to tell the team that I think it would be best if I sit out the rest of the day, so that I can be prepared for this long, tough race that’s going to happen (Sunday).”

If Gordon starts Sunday’s race and subsequently turns the car over to Smith, he’ll collect driver championship points based on the car’s finish. Even if he can’t take the green flag, Gordon won’t need a medical exception to preserve his Chase for the NASCAR Sprint Cup eligibility because he qualified the car.

If Gordon is in the car, he’ll start 27th, the position on the grid he earned Thursday. If Smith starts the 600, he will drop to the rear for the green flag because of the driver change.

“I know it’s not easy for him,” Gustafson said, “but I know (Sunday) he’ll do everything he can to get in and go. These guys do a lot physically, and he’s done it over a long period of time.

“His body has taken a long toll. It’s amazing he’s in as good shape as he is and is in as good condition as he is week in and week out. I’m sure he’ll fight through this as best he can.”