Aric Almirola subbed for Scott Speed in Happy Hour at New Hampshire Motor Speedway on Saturday.
According to Red Bull General Manager Jay Frye, Speed was suffering from flu-like symptoms and went to the infield care center for treatment.
"We'll see how Scott does tonight and go from there," Frye said. "We hope it's a 24-hour bug but we've asked Aric to stay overnight as a precautionary measure."
Speed qualified 28th for Sunday's Sylvania 300. He was posted as 33rd fastest in morning practice with a time of 128.576 mph.
Fox News First
Get all the stories you need-to-know from the most powerful name in news delivered first thing every morning to your inbox.
By entering your email and clicking the Subscribe button, you agree to the Fox News Privacy Policy and Terms of Use, and agree to receive content and promotional communications from Fox News. You understand that you can opt-out at any time.