Cheltenham Gold Cup winner Don Cossack will miss the Punchestown Festival in Ireland with a tendon injury.
The horse, trained by Gordon Elliott, was set for a keenly-awaited rematch with Cue Card in the Punchestown Gold Cup on Wednesday.
Cue Card, who fell three fences from the finish in last month's Gold Cup, is now favourite for the title in Ireland.
Cheltenham World Hurdle winner Thistlecrack has been ruled out of the Champion Stayers Hurdle with lameness.
Thistlecrack, like Cue Card is trained by Colin Tizzard.