Hamlin, 32, was going against Joe Gibbs Racing teammate Joey Logano for the lead in the final lap of the Auto Club 400 when they made contact and both spun. Hamlin's car hit a retaining wall.
He walked away from the wreck but then laid down on the track. He was taken to a hospital and subsequent examinations led to a diagnosis of a compression fracture of the lower back.
JGR on Wednesday announced that Hamlin would be out of racing for at least six weeks but didn't name a replacement driver.
"If me getting back in a car was based on pain tolerance then I would be in the car next week. There's just more to it that I can't control," Hamlin said in a Twitter post.
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