Phoenix Thoroughbreds ownership group announced Monday that Gronkowski the horse developed a fever over the weekend and is unable to make the journey to Churchill Downs.
Gronkowski, who is part-owner of the horse, tweeted about his namesake.
It's unfortunate Gronkowski the horse will not be able to race in the upcoming Kentucky Derby due to an illness. I fully support what is best for the horse. I know he will come back strong and healthy and I am excited to see him race again very soon.— Rob Gronkowski (@RobGronkowski) April 23, 2018
Earlier Monday, the ownership group tweeted that the horse was treated with antibiotics and "is doing well."
We very much regret that #Gronkowski will miss the @KentuckyDerby after spiking a fever over the weekend and being treated with antibiotics. He can't make the long journey to Louisville but is doing well pic.twitter.com/71CqtWnDub— Phoenix Thoroughbred (@PhoenixThoroug1) April 23, 2018
The horse had been scheduled to fly to Kentucky this upcoming weekend.
Tom Ludt, head of operations for Phoenix Thoroughbreds, told ESPN that the shelving of the horse for the Derby has no effect on Gronkowski's investment, saying the family "bought in for the long term."
"They are still excited and hopefully we still make the Belmont," Ludt said.
The equine Gronkowski qualified for the 1¼-mile Kentucky Derby with a victory at the Burradon Stakes in Newcastle, England. He has never raced more than a mile, nor has he raced on dirt.
ESPN's Darren Rovell contributed to this report.