Constitution Hill is in a veterinary hospital after suffering a suspected bout of colic.
Last year’s Champion Hurdle winner missed this month’s Cheltenham Festival after a poor workout.
Trainer Nicky Henderson said it had been a “traumatic few days” and the seven-time Grade One winner was “not completely out of the woods yet”.
But he hoped the seven-year-old would be able to return to his Berkshire stables in the coming days.
It means he is extremely unlikely to make his intended return at the Punchestown Festival on 3 May.
A statement from Henderson on X on Sunday read: “We’ve had a few traumatic days with poor Constitution Hill as he had to go to the veterinary hospital on Wednesday night in order to monitor suspected colic.
“I’m pleased to say that they have managed to avoid surgery so far and this morning he is being reintroduced to a normal diet and if this goes well he could come home in the next day or so.
“We’re not completely out of the woods but very hopeful that he’ll soon be back, which will be an enormous relief.
“This will obviously interfere with our plan to get to Punchestown which is very sad but the only important thing at the moment is to get him safely home.”
AP McCoy called Constitution Hill “the horse of a generation” after last year’s Champion Hurdle win.
But he has only raced once this season, on 26 December at the Christmas Hurdle at Kempton, where he won easily under jockey Nico de Boinville.
