The 19-year-old Californian was in the midst of a third lap during a simulation qualifying run when his #18 Dale Coyne Racing Honda snapped around and hit the outside wall on the exit of Turn 2.
After making contact with the wall, the back of the car the began to lift and it skated down the backstretch on the left side before coming to a stop in the middle of the track.
"I don't know [what happened] to be honest," said a bewildered Siegel after being checked and released from the infield medical centre. "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.
Siegel, who currently runs full-time in Indy NXT and is vying for his second start in the IndyCar Series, was able to walk away from the accident after receiving assistance – due to car positioning and the aeroscreen – from the accident. There were some patch work needed to the track where the suspension of Siegel's car dug into the surface.
The incident happened roughly 90 minutes into the day, with Siegel only running 15 laps with a best of 229.813mph to put him 28th.
He becomes the third driver to crash this week, with Chip Ganassi Racing rookie Linus Lundqvist and Andretti Global’s Marcus Ericsson, the 2022 Indy 500 winner, involved in separate incidents on Thursday’s running.