Noel Meade's Randox Health Grand National contender A Genie In Abottle was found dead in his stable on Friday.
The seven-year-old's death is a mystery to his connections at present.
He was owned by Gigginstown House Stud and had been around 50-1 for the National but was sent off 4-1 favourite for the four-mile National Hunt Chase at Cheltenham last season where he finished fifth.
"We've no idea what happened. He was okay in the morning and dead in his box at lunchtime. It's just one of those things," said the Gigginstown's spokesman, Eddie O'Leary.
