On doctors’ advice, Kyle Larson will not race in Sunday’s STP 500 at Martinsville Speedway (1 p.m. ET on FOX Sports 1), after fainting during an autograph session on Saturday afternoon.

Regan Smith will take Larson’s place in the No. 42 Chip Ganassi Racing Chevrolet.

“After fainting yesterday at an autograph session in Martinsville, Virginia, Kyle Larson was first evaluated at a local hospital in Martinsville and ultimately evaluated at a Charlotte hospital,” Chip Ganassi Racing with Felix Sabates said in a statement released Sunday morning.

“Although all tests came back negative and Larson feels completely fine, the doctors felt he should be held for more testing today. Subsequently, Larson will be unable to race today in the STP 500 in Martinsville.”

Smith hasn’t had a full-time NASCAR Sprint Cup Series ride since 2012, but he has raced in a substitute role for Dale Earnhardt Jr., Tony Stewart and most recently for Kurt Busch.