Dale Earnhardt Jr explains decision to retire from NASCAR Cup

The 42-year-old had indicated earlier this year that he would wait a few months to assess his form and feelings after returning to competition following his long absence due to a concussion-related illness last season before deciding whether to extend his Hendrick Motorsports contract.

Earnhardt then announced on Tuesday that this would be his last season of full-time racing, and later revealed that he had made his mind up almost a month earlier - informing team boss Rick Hendrick on March 29.

"The reason I reached this decision is really simple - I just wanted the opportunity to go out on my own terms," Earnhardt said

"Every driver thinks about retirement and what they think that looks like for them.

"I wasn't thinking about it too much until the last couple of years.

"Once I realised how delicate things are, it's something I had to start thinking about quite seriously.

"I had a lot to think about over the last several months, and I was not sure I would have the opportunity to compete this season.

"It's been a blessing and it's been a gift to be at the racetrack.

"During my rehabilitation, I was given something that I wasn't accustomed to, and that was time - time to understand what's important to me, time to realise the incredible support system I have.

"I just wanted to be able to make that decision on retiring myself and not have it made for me."

Though this will be Earnhardt's last year at Cup level, he will honour a commitment to take part in two races in the second-tier Xfinity Series for his own JR Motorsports team in 2018.

Asked if he could foresee taking the JR team up to the Cup series, Earnhardt intimated he preferred to see it remain as a feeder squad.

Drivers who have used JR Motorsports as a springboard towards the top class include Martin Truex Jr, Brad Keselowski, Danica Patrick and Chase Elliott.

"I really enjoy being in the Xfinity Series," Earnhardt said.

"There is a reward that I get from helping people achieve their goals and get to the next level.

"That's really so rewarding to me, really even greater than the wins, to see somebody get a job somewhere on the Cup level, getting an opportunity to step up.

"We're giving people that platform, that springboard, and I don't know if you could replicate that anywhere else."

Hendrick said a replacement for Earnhardt in 2018 had not been chosen yet.

"We've got a lot of people to consider - our partners, our sponsors," he said.

"We've been talking to them. Priority number one is to get everything prepared, get today over with.

"We'll take time to decide what we do."