Kahne, who announced in August he will stop racing full-time to focus on his son and his sprint auto teams, went to the Darlington infield care center after the 500-mile Labor Day weekend race with symptoms of dehydration.
Driver Kasey Kahne celebrates after winning the NASCAR Sprint Cup Series Coca-Cola 600 autorace in Concord, North Carolina May 27, 2012.
Smith finished 20th in Monday's race at Indianapolis Motor Speedway.
"I just can't control the temperature in my body and my heart rate", Kahne said at Indianapolis during his media availability on September 7. But while he searches for a solution, Kahne insisted on Wednesday that his racing career is not over - and will continue in some form. We're still trying to figure that out.
Ten races remain in the 2018 Cup Series season. I love racing. I've been racing most of my life and I'm not ready to give it up. He is also slated to run events at Richmond and the Charlotte Roval.
The Brickyard 400 was Regan Smith's first Cup Series race since filling in for an injured Aric Almirola at Richard Petty Motorsports past year. He admitted that the issue played a role in his decision announced last month that he would step away from fulltime NASCAR racing at the conclusion of the 2018 season.
Temperatures are expected to be near 100 degrees at Las Vegas Motor Speedway for Smith's second start of the season. He won last year's Brickyard 400 in his sixth and final season driving for Hendrick Motorsports to secure a playoff berth. This top 14 finish was his fourth place finish in the July race at Daytona International Speedway, a race that he looked like he had a good chance to win as the laps clicked down toward the end.
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Kasey Kahne will miss at least three of the next Monster Energy NASCAR Cup Series races as a result of an ongoing hydration issue.