Rahal was team-mates with Justin Wilson, who lost his life in an IndyCar crash at Pocono in 2015, at Newman/Haas Racing for the 2008 season following the unification of series.
In the aftermath of Justin’s death, Rahal went to huge lengths to organise a charity auction on eBay to benefit his wife and daughters.
Following Stefan’s crash in practice at Indianapolis on Monday, in which he suffered a fractured vertebra that ruled him out of the race after qualifying 25th, Rahal received a call from Wilson’s team boss Dennis Reinbold.
Rahal was also team-mates with Justin at Dreyer and Reinbold for one race at Iowa in 2010, and that helped steer his decision to step into Stefan’s #24 Cusick Motorsports entry on Sunday.
“In some other situations, I don't think that it would have excited me as much,” said Rahal.
“But being that it was Stef, and being that it was a Wilson, and in the situation that it was in, I just felt like it was my calling to jump in and help.
“I don't feel good about filling in for an injured driver. I feel for Stefan. It's a very unfortunate situation.
“When I saw the accident, I was very concerned for his back right away, when I saw the angle of the accident and, unfortunately, I'm aware of those things because of being a taller driver. It is an issue we I feel like have a little more frequently.”
Source: Autosport