A spokesman for the driver said Labonte was taken to a hospital by ambulance and was to be held overnight for observation.
Labonte was scheduled to drive the No. 51 Chevrolet for Phoenix Racing at Atlanta Motor Speedway. He'll be replaced in the car by Mike Bliss.
Labonte's consecutive starts streak came to an end earlier this season at 704 races when JTG Daugherty Racing used AJ Allmendinger at Kentucky in June instead of Labonte.
The 2000 NASCAR champion had not missed a start since he began racing full time in the Cup Series in 1993. He's won 21 races Cup races.