Dale Earnhardt Jr. has effectively been ruled out of NASCAR Sprint Cup title contention after announcing that he will miss the championship's next two races.

His team, Hendrick Motorsports, revealed on Thursday that Earnhardt, 38, has been diagnosed with a concussion following his involvement in the multicar final-lap crash at Talladega last week.

He will miss this weekend's Cup race at Charlotte and the following event at Kansas as a result, with Regan Smith replacing him in the No. 88 Chevrolet Impala. AJ Allmendinger, recently reinstated to NASCAR eligibility after completing a drug rehabilitation program, will drive in place of Smith in the Phoenix Racing Chevrolet.

Earnhardt, whose late father won seven Cups during his career, is currently 11th in the Chase for the Sprint Cup, 49 points behind leader Brad Keselowski.

Although the concussion was sustained at Talladega, it was a relapse after he'd had an accident in a test at Kansas more than a month ago. Earnhardt blew a right front tire and crashed in Turn 1.

“I guess I'll just started out with where this all began,” he said. “We had a test at Kansas about five weeks ago and blew a right front tire going into Turn 1. I remember everything about that accident, but you know your body and how your mind works, and I knew something was not quite right.

“I decided to just try to push through and work through it. I've had concussions before, so I knew what I was dealing with.”

Once the Chase started, Earnhardt said he was not quite back to 100 percent, but close. He estimated feeling 80 to 90 percent at Chicago but back to 100 by the time of Talladega.

The accident hit him in a weird way, as he was caught up in the middle. He said the Kansas crash registered at 40Gs, with the Talladega one only (relatively speaking) at 20G, but still was unsettling enough to require further evaluation.

“In the accident at the end of the race, I was hit in the right rear quarter panel. It was an odd kind of collision,” he explained. “The car spun around quick and disoriented me. I knew I'd sort of regressed. I'd had something of a setback, and I knew I had re-injured myself for lack of a better way to describe it.

“It didn't feel – it wasn't half the impact that I had at Kansas. But it was enough to cause me some concern. I went a couple days wondering how my body would react. Waited for my body to process what was happening. I still had headaches on Wednesday; that was the only symptom I was having.”

From there, Earnhardt met with his sister and neurosurgeon Dr. Jerry Petty to figure out the due course of action.

“I contacted my sister and we talked about seeing a neurosurgeon, we got steered toward Dr. Petty,” he said. “I met with him, ran through a couple tests. Did an MRI, everything looked good. I was really honest with how I felt and the whole process from Kansas on.

“He couldn't, in good conscience, clear me to race this weekend. I trust his opinion and it's why I went to see him. I've went through a lot of injuries before. When he told me I don't need to be in the car and take a couple weeks off, that's what I need to do.”

Earnhardt will not only miss the races, but he won't be at the track in either of the next two weeks, saying he didn't want to be a distraction. His crew chief Steve Letarte said Smith has already got a seat fit in the car, and will make other adjustments to the car as needed at the track this weekend.

Summed up succinctly, Earnhardt said, “I knew having them two concussions back-to-back was not a good thing. I needed somebody to tell me that because I was going to have a hard time making that decision for myself.  I feel perfectly fine, but I don't want to keep getting hit in the head.”