The Mark Bradstock-trained eight-year-old has gone to Newmarket for further veterinary assessment after suffering an injury and it is believed he will miss the rest of the campaign.
Coneygree, who looked so impressive on his return to action at Sandown in November, had been in the frame to run over Christmas in either the King George VI Chase at Kempton or in the Lexus Chase at Leopardstown.
But plans have been derailed after he suffered what is understood to be slab fractures in both hocks, although it is not thought to be a career-threatening setback.
Sara Bradstock, the Oxfordshire trainer’s wife and assistant, said: “He is injured and will not run in the King George or the Lexus. The Christmas run is out.
“He is in no distress and walked on to the box sound. The vets at Newmarket will have a good look at him and we’ll see what they discover – it will be a day or two before we have any news.
“They’ll probably scan him and we’ll see what the extent of the damage is.
“We know the engine is there, but the long legs that serve him so well on the racecourse are a little bit fragile.
“Everyone knows I think the world of this horse, which is why we’re being careful.
“There will be no corners cut. He will be back, but at this stage I can’t tell you when that will be.”
Coneygree missed an intended appearance in last month’s Hennessy Gold Cup at Newbury after he suffered a foot problem, but Sara Bradstock said the latest setback was unrelated.
Coneygree’s finest hour at Cheltenham saw him become the first novice to win the Gold Cup in 41 years, after Captain Christy in 1974.
He was ridden by Nico de Boinville, who said: “Obviously it is very disappointing, especially for the whole Bradstock team at home and connections, as he has been such a superstar horse.
“That’s horse racing for you, it’s what makes the good days worthwhile.”
Willie Mullins is responsible for three of the top four in the market – last season’s runner-up Djakadam, Don Poli, and Vautour – with the Gordon Elliott-trained Don Cossack the other vying for favouritism.
Ladbrokes have three co-favourites at 5-1 with Vautour an 11-2 chance in a revamped market.
“It’s a big blow to the race. There’s no way of swerving that, and it’s a blow to those of us who thought we were in a vintage era,” said David Williams of Ladbrokes.
“It is very difficult to escape the feeling the Irish have got an enormous stranglehold on the race now - in fact it looks a bit of a benefit for them.
“Djakadam, Don Cossack and Don Poli are co-favourites at 5-1 and Vautour is 11-2. Literally, you can throw a handkerchief over the front four.”