Jenson Button suffered from heat exhaustion and nearly retired on his NASCAR debut, before finishing 18th.
The former F1 world champion, 43, said he feared fainting while driving his Ford Mustang during the 68-lap race at the Circuit of Americas in Texas on Sunday.
"Finished 18th after almost stopping because I had heat exhaustion. It was so hot. I don't have a fan in my seat, which really didn't help me too much," Button said.
"I stopped twice for a minute. They put ice on me, gave me loads of water, and I went back out.
"I was so close to getting out of the car because I thought I was going to faint. I must have drank eight (or) nine bottles of water during the race.
"The team kept me calm, and it's the reason why we got a good result in the end. So, I was happy."
Button will next compete in the inaugural Chicago Street Race on July 2 before racing at the Indianapolis Motor Speedway road course on August 13.
