The 19-year-old lost control of his #18 Honda while negotiating Turn 2 on the third lap of a qualifying simulation at The Brickyard.
Siegel began to spin and was backwards by the time he made contact with the wall, before his Dale Coyne Racing entry was picked up and turned over.
It skated down the back straight on its side before coming to rest still upside-down, after which it had to be righted by the safety crew so Siegel could get out.
He was taken to the circuit medical centre per protocol and released, while the track required repairs due after Car #18 had ground into the surface.
“I don’t know [what happened] to be honest,” he said. “I’ll have to look at it closer.
“I had one snap of oversteer that I caught and then turned back in and spun, and I’m not exactly sure why.”
After watching the replay, he added, “[I[ Feel bad for the team that’s been working so hard for so long for this and just kind of threw it away, so not at all happy about that one.
“But, we’ll move forward and see if we can get back out and qualify for the race tomorrow.”
Hear reaction from @nolan_siegel following his scary incident.
📺: #Indy500 practice on Peacock pic.twitter.com/z2oe7eU6w5
— NTT INDYCAR SERIES (@IndyCar) May 17, 2024
DCR is running two cars in this year’s Indy 500, the other being the #51 entry driven by Katherine Legge, with Siegel expecting he will need a back-up chassis.
“We’re probably going to have go back to the spare car and we don’t know exactly where that’s going to be,” he said.
“I’ll look into what I can do differently.
“I’m fine. I feel like I can go back out and we’ll have a chance at making the race at least, but certainly a setback we didn’t need so my apologies to everyone.”
Fast Friday sees drivers run with an extra 100 horsepower thanks to higher turbo boost pressure in preparation for qualifying weekend.
Thus far, the fastest laps of the day have been run above an average of 234mph.