Jeremy Noseda admitted to being "shocked and surprised" after owners Phoenix Thoroughbreds removed all the horses they had in training with the British handler.
One-time Kentucky Derby hope Gronkowski was the highest profile Phoenix-owned horse based with the Shalfleet team in Newmarket.
The three-year-old won for the third time this year in the Burradon Stakes at Newcastle in March, after which Noseda confirmed his charge would be trained for the 'Run for the Roses'.
He is named after New England Patriots tight end Rob Gronkowski, who later acquired a share in the horse in anticipation of watching him run at Churchill Downs.
However, his American dream was dashed when he was ruled out after spiking a fever and it now appears he has run his last race for Noseda.
The trainer posted on Twitter: "The Phoenix-owned horses have left Shalfleet.
"I am shocked and surprised by their decision. I have no reason or explanation for the decision."
The Phoenix-owned horses have left Shalfleet. I am shocked and surprised by their decision. I have no reason or explanation for the decision.— Jeremy Noseda (@JeremyNoseda) May 8, 2018