The Briton had qualified 19th for his first Indy 500, but lost ground at the start of the race and was running in a net 26th when he lost the rear of the car at Turn 2 on lap 69.
The car spun through 270 degrees, striking the SAFER barrier with first the nose and then the left side, sustaining heavy damage.
Ilott exited the car without assistance, but his hand and wrist were strapped when he emerged from the infield medical centre and he has not been cleared to race on Belle Isle this weekend.
The former F2 racer will be reevaluated next week, with Ferrucci set to replace him after finishing 10th in the Indy 500 last weekend for Dreyer & Reinbold Racing.
“Obviously I am devastated not to be racing this weekend in Detroit,” said Ilott.
“After speaking with the doctors and specialists here in Indy, the damage to my hand was slightly worse than when first looked at it.
They suggested that the long-term healing was the top priority and any damage that could be done in the short term by racing would be a longer-term problem.
“After learning this I agreed with the medical team’s decision that I would not be cleared and would spend more time healing. Although I would have loved to be racing, I wanted to preserve myself and focus on my health.
“I spoke with [team co-owners] Ricardo [Juncos] and Brad [Hollinger] and we came to a same conclusion for the benefit of the team.
“I will be with the team this weekend and supporting Santino and providing any guidance I can. I am sorry that I won’t be in the car this weekend but know this is the right decision.”
“This is a very difficult scenario for Ilott and JHR,” said Juncos.
“Together we are looking at the long-term view, so keeping Ilott out of the car to take the necessary time to heal was most important, so we support IndyCar’s evaluation.
Callum has already proven to be a strong contender this year and we want to keep building on that, so we all agree this is the best decision for this weekend.”
For Ferrucci, it will be a third start of the season with as many different teams.
Prior to Indy with Dreyer & Reinbold, the 24-year-old subbed for Jack Harvey at Rahal Letterman Lanigan Racing in Texas, when the Briton wasn’t cleared to race following a practice crash.
Last year, racing a third RLL car, he finished sixth and 10th at Detroit in what was then a double-header.
“Although I am happy to be back in the car, it’s unfortunate for Callum under the circumstances,” said Ferrucci.
“I hope his hand heals really quickly and he is back on track soon.
“I’m just here to help with the team and see if we can get them a really good result and bring in some different knowledge from my experience in Detroit.
“I am looking forward to having some fun and carrying the momentum I have from Indy. I can’t thank the guys over at Juncos Hollinger enough with in trusting me this weekend and hopefully it goes really smoothly.”
Juncos said Ferrucci “will be a great assist to our team”.
“This is a tough moment for all of us here at JHR, but we are all confident this is what’s best for the health and healing of Callum,” added Hollinger.
“The support Callum has for this team and the support we all have for Callum, shows the unity of everyone at JHR.
“We are all here to fully support Santino this weekend and thank him for stepping in on such short notice.”
