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 — teammate Jimmie Johnson even caught a lift on the window back to the garage.
He sought out personal physician Dr. 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.
"If we can't, we'll let him go out and drive a lap or two and see how that goes, and if that goes well, we'll probably clear him to race," Petty said.
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 on the last lap of 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 longshot anyway because of a mediocre start to the Chase.
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.
Team owner Rick Hendrick praised Earnhardt for seeking medical care this week.
"I think a lot of guys would try to play hurt," Hendrick said. "I applaud Dale for raising his hand and going in there and getting checked out."
O'Donnell said NASCAR will likely review the Kansas accident and see if series officials should have handled Earnhardt's care differently.
Other sports have struggled with their handling of concussion, especially football and hockey.
After years of denying any connection between head injuries suffered on the field and later brain injuries, the NFL now has a protocol before players can return if they show symptoms of a concussion. The NFL is also being sued by more than 3,000 former players who claim it didn't do enough to protect them.
O'Donnell said drivers have to take some responsibility for their health, as well.
"The process of an evaluation for any athlete or driver, it's not just NASCAR making the call," O'Donnell said. "It has to be the driver as well letting us know how he's feeling. We'll look at Kansas and see what we may be able to do better."
Nationwide Series driver Eric McClure was held out six weeks this season with lingering effects of a concussion suffered at Talladega. McClure said the concussion he sustained in the May 5 race was the third of his career, and the frequency was one of the main reasons his doctors and NASCAR officials made him sit out for an extended period of time.
Sprint Cup Series points leader Keselowski knows how hard it is for a driver to consider sitting out a race. He broke his ankle in a crash while testing last summer, and although he had a backup driver on standby, he didn't miss a Cup start.
"It's your worst fear, to not be in the race," he said. "Missing the show is terrible."