On his weekly podcast, Dale Earnhardt Jr. set no timetable for his return to the cockpit of the No. 88 Hendrick Motorsports Chevrolet.

Earnhardt has missed the last two races because of concussion symptoms, including nausea and lack of balance. He also will miss the upcoming race at Pocono Raceway on Sunday.

Speaking on his weekly "Dale Jr. Download" podcast, which was released Monday afternoon, Earnhardt said he did not yet know when he would drive again. Earnhardt said he is working on rehabbing from his concussion, following a protocol from his doctors.

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"Myself, I've been working on the exercises -- physical and mental exercises that they gave me, from my doctors," Earnhardt said. "That stuff takes about 2 hours, 2½ hours, each day. I've got to do it every day. There's worse things to have to do. Some of it's tedious. Some of it's pretty tough. Some of the visual stuff is pretty tough."

Earnhardt said drivers can race with some forms of injuries, but not concussions. "There's certain things you can race through," he said. "But one of the things that you cannot race through is concussion-like symptoms. The balance deal is a critical part of being able to drive a race car."

Then Earnhardt added, "This process is going to take a little bit longer. I think that's what I was trying to convey when I was telling you guys how I was going to take this slow and listen to the advice of my doctors."

Earnhardt has a prior history of concussions and so is being appropriately careful about not rushing the process of recovery.

"I'm not going to go against that advice, no matter what," he said. "I can't play around at this age. With my history, I definitely don't need to get cute."

Earnhardt said he would have another medical update next Monday, but for now, he's still on the sidelines.