The Hendrick Motorsports driver tweeted that his right-front tire has a puncture in it, and his No. 88 Chevrolet will start at the back and forfeit his 18th starting position.
Earnhardt shared a photo of the tire on Twitter and noted that his team would be able to replace only the right tire, which could make for some wonky handling on the abrasive 2-mile oval.
Under a new rule this season, NASCAR mandates that drivers must start the race on the tires they used to qualify.
Switching tires sends the car to the rear for the green flag, which happened to Denny Hamlin at Phoenix Raceway last week.
Earnhardt still isn’t a fan of the new policy, particularly at a track such as Fontana, whose razor-sharp surface tears apart tires.