Sam Spinner will not run again this season due to a pelvic injury.
Trainer Jedd O'Keeffe was told the diagnosis by the vet this morning and announced the news via social media.
The problem, picked up in an ultrasound scan, stops the seven-year-old from trying to continue his unbeaten start to his chasing career.
Runner-up in the 2019 Stayers' Hurdle, Sam Spinner has won all three of his races over fences, accounting for highly touted Windsor Avenue in impressive fashion last time out.
O'Keeffe believes his stable star, who was a leading fancy for the RSA Chase at The Festival, could have developed the issue during the 38 length success.
"He was doing his first steady canter back and my assistant Leanne Kershaw felt something was amiss straight away," he said.
"We were told this morning that he has a small crack in his pelvis.
"I think it must have happened in his last race at Doncaster.
"We were hoping to go to the Towton or Reynoldstown novice chases next on the way to the RSA.
"While I'm very disappointed, I'm pleased we found it so quickly with an experienced rider on board.
"Sam Spinner will have some time in his stable before returning to controlled exercise.
"It's a shame for his owners and everyone at the yard, he has been an incredible horse for us.
"Hopefully when he is back to full fitness we can get back to where we were."
In 19 races under Rules, Sam Spinner has won more than£250,000 for connections.
He was sent off favourite for the 2018 Stayers' Hurdle, when he finished fifth under regular rider Joe Colliver.
Ante-post RSA market leader, Champ, is entered to run at Cheltenham on New Year's Day.
