Trainer Jeremy Noseda told RacingPost.com that the horse, named Gronkowski, suffered an unspecified "setback."
"We've had a minor setback and we will know where we are in the next 24 hours," Noseda told the website on Monday.
The horse, which is partly owned by the five-time Pro Bowler, had been scheduled to fly to Kentucky this upcoming weekend.
Gronkowski qualified for the 1¼-mile Kentucky Derby with a victory at the Listed Burradon Stakes in Newcastle, England. He has never run more than a mile, nor has he raced on dirt.