CONCORD, N.C. – Dale Earnhardt Jr. knew he had suffered a concussion in an August crash so jolting that other drivers tweeted about it immediately after the impact.

Earnhardt was too stubborn to see a doctor. He was too worried he would be yanked from his car, derailing his long-suffering Sprint Cup Championship hopes.

So he kept it a secret until a 25-car accident on the last lap Sunday at Talladega left him with a lingering headache.

NASCAR’s most popular driver consulted a neurosurgeon, who found Earnhardt had indeed suffered two concussions in six weeks and could not be medically cleared to race. Earnhardt will sit out the next two weeks, at Charlotte and Kansas, ending his championship chances.

“I would love to race this weekend, and I feel perfectly normal and feel like I could compete if I were allowed to compete,” Earnhardt said Thursday. “But I think that the basis of this whole deal is that I’ve had two concussions in the last (six) weeks, and you can’t layer concussions. It gets extremely dangerous.”

A decade ago, it was Earnhardt who helped spur changes in how NASCAR handled drivers showing signs of a concussion.

He self-diagnosed a concussion from an accident at California, but only weeks later revealed in an interview that he’d been having difficulty focusing and communicating with his crew chief. Within days of his admission, NASCAR strengthened its commitment to keeping drivers with concussions off the track.

NASCAR ruled that drivers unable to drive their car back to the garage after an accident had to make a mandatory trip to the infield care center. The attending physician could then refer a driver to a neurosurgeon if they suspected a concussion.

Clearance to race after suffering a concussion is not given until after a driver obtains a medical release.

Hendrick Motorsports tabbed Regan Smith to replace Earnhardt in the No. 88 Chevrolet the next two races. Smith had been scheduled to drive the No. 51 for Phoenix Racing in Saturday night’s race at Charlotte Motor Speedway, but A.J. Allmendinger will now drive that car in his first start since his July 7 suspension for failing a random drug test.

The crash at Talladega dropped him to 11th in the Chase standings, and missing two races means he’ll most certainly finish last in the 12-driver Chase race. He’ll also end his streak of 461 consecutive starts, which is the fifth-longest active streak in the Sprint Cup Series. 

QUALIFYING: Greg Biffle won the pole for Saturday night’s race, turning a track-record lap of 193.708 mph in his No. 16 Ford.

Biffle will start alongside Mark Martin on the front row for the fifth race in NASCAR’s Chase for the Sprint Cup title.

It was Biffle’s 12th pole overall and third this year, but his first ever at Charlotte. Ryan Newman was third, followed by Clint Bowyer and Jimmie Johnson.

Points leader Brad Keselowski qualified 20th.