From JGRs Facebook page:
Joe Gibbs Racing driver Denny Hamlin was evaluated today by Dr. Jerry Petty of Carolina Neurosurgery & Spine Associates after suffering an L1 Compression Fracture during an accident on the final lap of Sundays NASCAR Sprint Cup Series Auto Club 400 at Auto Club Speedway.
Dr. Petty determined that Hamlin will not require surgery, but will need time to properly heal, which is estimated around six weeks time. Dr. Petty will make the determination when Hamlin will be able to return to racing this season.
No decision has been made on a replacement driver for Hamlin during his absence from the NASCAR Sprint Cup Series.