The final lap wreck at Talladega on Sunday has effectively ended Dale Earnhardt Jr.'s Sprint Cup Chase season, after it was revealed that he will miss at least the next two races of the season following a diagnosis of concussion.

In a press release from his Cup team Hendrick Motorsports, it was revealed that Earnhardt was confirmed as suffering from the after-effects of concussion following a medical examination by Dr. Jerry Petty on Wednesday afternoon in Charlotte. Earnhardt had been complaining of headaches in the intervening days since the end of Sunday's race.

Under NASCAR rules, a confirmed case of concussion requires a driver to be sidelined for a period of time on safety grounds. Earnhardt was not reported as injured on the day, and even stopped to give his team mate Jimmie Johnson a lift back to pit road after the accident.

It also emerged that it appears Earnhardt suffered an earlier concussion at the end of August after a hard crash at Kanas during official tyre tests at the resurfaced speedway. That concussion was not diagnosed at the time, but the fact this Talladega makes it two such blows to the head in six weeks is enough to concern the series medical staff into demanding that Earnhardt be parked up for the next fortnight for his own good.

As a result, Earnhardt will be absent from both this Saturday night's Bank of America 500 at Charlotte Motor Speedway as well as week's race at Kansas Speedway. It brings to an end his record of 461 consecutive Sprint Cup race starts and will be the first NASCAR Cup race without an Earnhardt competing in it since September 1979.

It isn't clear how long Earnhardt will be out of the car. Although two weeks is the minimum, it might be much longer before he is given a medical release to compete once again.

In the Nationwide Series, driver Eric McClure had to sit out six weeks earlier this season with the lingering after-effects of a heavy concussion, also suffered at Talladega.

"There's not really a set timetable for those things and that's been the challenging thing," said McClure at the time. "That's what kept me from coming back was the lingering symptoms."

With only six races remaining in the ten-race Chase, and having already taken a hefty hit in points and positions following the last-lap wreck at Talledega on Sunday, even two races out effectively ends Earnhardt's hopes of featuring in the battle for the 2012 Sprint Cup Series championship.

The team has announced that Regan Smith will take over the driving duties of the #88 car in Earnhardt's absence.

Smith has been driving the #78 Furniture Row Racing car this season, but was recently told that he had lost the ride for 2013 and would be replaced by Kurt Busch starting at this weekend's race in Charlotte.

It had previously been announced that Smith would effectively swap seats with Busch and take over the driving duties of the #51 Phoenix Racing car, but the news of Earnhardt's concussion has changed those plans and left James Finch's small team needing an experienced Cup driver at very short notice.

They've plugged the gap by turning to AJ Allmendinger, the driver who was suspended from NASCAR competition over the summer after failing a random drugs test, but who was confirmed last month as being eligible to drive once again after successfully completing the series' "Road to Recovery" rehabilitation program.

Allmendinger was first from his previous team, Penske Racing, after the drugs test result was confirmed. Coincidentally, he had been in the team's #22 car previously driven by Kurt Busch before he and the team fell out at the end of the 2011 season, making this the second time that Allmendinger will have followed Busch into the same race seat in under 12 months.

There had been speculation that Busch himself might not be able to compete this weekend at Kansas, after a bizarre incident early in the race at Talledega where he drove away from track safety officials with an EMT kit still on the top of his car, apparently ignoring instructions from race control.

However, NASCAR were satisfied that being excluded from the race was sufficient penalty and accepted his explanation that he had removed his helmet when talking to the track workers and was unable to hear orders from the tower or his pit wall, and that therefore he would not be given an additional race ban penalty.