Champion Bumper winner Fayonagh has been put down after breaking a hind leg on the gallops on Wednesday morning.
The Gordon Elliott-trained mare, who only suffered one defeat in her six races, was working under Davy Russell when the accident occurred.
She had made a successful hurdling debut only recently and was expected to take high rank among the novices this season.
Elliott told his Betfair column: "I'm devastated to announce that Fayonagh broke a hind leg this morning while doing a routine piece of work under Davy Russell at Skryne gallops and had to be put-down.
"As a dual Grade One-winning mare she was an exceptional talent and the sky was the limit with her.
"Needless to say, we are all heartbroken and our thoughts are with the connections at this time."