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 about it. 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 sought medical attention from a neurosurgeon, who found Earnhardt had indeed suffered two concussions in six weeks and could not be medically cleared to race. Earnhardt said Thursday he 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. ‘‘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.’’
Earnhardt’s first concussion this season came in an Aug. 29 wreck during a tire test at Kansas. His crash into the wall when his right front tire failed was so hard that Brad Keselowski immediately tweeted about it. Earnhardt was seen after the accident in the back of an ambulance, but was not treated in the infield care center and did not seek examination elsewhere.
He attended a Redskins exhibition game that night, but admitted Thursday he knew he suffered a concussion.
‘‘You know your body, and you know how your mind works, and I knew something was just not quite right,’’ he said. ‘‘But I decided to just try to push through and work through it. I’d had concussions before and knew exactly kind of what I was dealing with.’’
Earnhardt said he regrets not seeing anyone about that concussion, but admitted to crew chief Steve Letarte what had happened, and said he would not have raced the next weekend if he’d not felt well.
‘‘With the Chase coming up, I didn’t know how difficult — if I was to volunteer myself to get medical attention and be removed from the car, I didn’t know how difficult it would be to get back in,’’ he said. ‘‘But I was honest with Steve and told Steve, ‘When we get to Atlanta and if I don’t feel good, I’m going to be honest with you and tell you that we need to have something as a backup plan for me to get out of the car.’ ’’
He didn’t give himself the same leeway this week, when he suffered a lingering headache following the last-lap accident at Talladega. Although Earnhardt said the impact was half as hard as the Kansas hit, ‘‘I knew as soon as it happened that I had reinjured myself.’’
Earnhardt didn’t have to make the mandatory trip to the care center on Sunday because he was able to drive his car away from the accident.
Earnhardt sought out personal physician Jerry Petty, a neurosurgeon who consults with NASCAR and the NFL’s Carolina Panthers, on Tuesday and underwent an MRI on Wednesday, his 38th birthday. The MRI showed no damage, but Petty said Earnhardt was candid about his symptoms that last six weeks and he diagnosed a pair of concussions.
‘‘His eyes did what they were supposed to do, his balance tests and so forth are perfect,’’ Petty said. ‘‘The one test, the one symptom that is more important than all the tests is headache, and as long as there’s any headache, the brain is not healed.’’
Petty said Earnhardt will not be cleared to race again until he’s gone at least four days headache free, and goes through a test in which Petty tries to provoke a headache.
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, and AJ Allmendinger will now drive that car in his first start since his July 7 suspension for failing a random drug test.
This weekend’s race will be the first since Sept. 3, 1979, that will not include an Earnhardt in the field. Earnhardt’s father, seven-time NASCAR champion Dale Earnhardt, was killed in the 2001 Daytona 500.
Earnhardt, who snapped a 143-race winless streak this season that dated to 2008, opened the Chase as a strong contender to win his first Sprint Cup title. This injury ends his chances, which were a long shot anyway because of a mediocre start to the Chase.
The crash at Talladega dropped him to 11th in the standings, and missing two races means he’ll most certainly finish last in the 12-driver Chase. He’ll also end his streak of 461 starts, which is the fifth longest active in Sprint Cup.