At 7 a.m. Thursday morning, Regan Smith was making coffee and preparing to go work out at a local gym when he saw a text message from an unknown number on his phone.

"This is Steve Letarte," the text said. "Give me a call ASAP."

The 29-year-old didn't think much of the message until he got to the "ASAP" part. Smith called Letarte, the crew chief of Hendrick Motorsports' No. 88 team, and was informed he'd be driving the car this weekend at Charlotte in place of Dale Earnhardt Jr.

Smith hopped in the shower, skipped the gym and went straight to Hendrick's shop in Concord, N.C., where he was fitted for a new seat in preparation to substitute for NASCAR's most popular driver, who is out for at least two weeks with a concussion.

It was a wild turn of events for a driver whose tenure in Furniture Row Racing's No. 78 car ended last week and who was set to debut in Phoenix Racing's No. 51 car this weekend.

"The past four weeks have been about as up and down as any four weeks in my life," Smith said Thursday at Charlotte Motor Speedway, wearing No. 88 Amp hat and green Amp T-shirt.

Smith made it clear his main concern was Earnhardt Jr.'s health and recovery, but said he was excited to have an opportunity to drive a Chase-caliber car.

"I just want to do these guys proud and run as good as we can this weekend with this car," Smith said. "They're the same goals this team has every weekend: We want to go out there and try win the pole and try to win the race and try to be the fastest car in every practice. That's not going to change these weekend."

Smith, who hasn't spoken to Earnhardt Jr. yet, said he didn't feel any more pressure than usual. There's always pressure no matter what car a driver races, he said.

That said, Smith is well aware he's under more of a spotlight than ever before in his career.

"I do know Dale's got a huge following – Junior Nation is a big group of people," he said. "I've seen the good side of them before and the bad side. I'm glad to be on the good side for a couple weeks."