Sam Hornish Jr will race for Denny Hamlin in the Joe Gibbs #11 car at Auto Club Speedway today.
Denny Hamlin has been treated by a local hospital after a sinus infection he developed over the weekend began to effect his vision.
Doctors advised the driver to not participate in the 500 mile event at Fontana today.
Due to the treatment and symptoms Hamlin will step aside for Sam Hornish Jr, who will start at the back of the pack due to the driver change.
This should not effect Hamlin's chances at a Chase spot, as he is expected to win a regular season race without issue, likely giving him a berth in the NASCAR post season.