Buzz - winner of the Cesarewitch and a leading fancy for the Stayers' Hurdle at the Cheltenham Festival - has met with a significant injury setback.
The Nicky Henderson-trained gelding suffered what is feared to be a fractured pelvis when having his final spin before the Long Walk Hurdle at Ascot on Saturday, live on Sky Sports Racing.
He had advertised his Festival claims when landing the Coral Hurdle, also at Ascot, last month.
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Henderson said on Friday: "We think he's fractured his pelvis, we don't have too many details at the moment as it's just happened but he's suffered a pretty severe injury.
"He was just doing his last little spin for tomorrow and about 100 yards from the end - bang.
"We've had a lot of horses that have recovered from a fractured pelvis to race again. The immediate danger is that he doesn't have an internal haemorrhage, but we were lucky in that we had a vet there within minutes.
"I was encouraged - we all were - with how well he actually managed to load considering he was on three legs and he was being very sensible.
"There's nothing we can do in the short term for him, bar painkillers, but the vet is almost certain he's fractured his pelvis, the wing of the ilium probably.
"The most important thing is that he stays as still as possible and as long as he doesn't haemorrhage, which is the dangerous part, if he gets through that it's just a matter of standing still for quite a long time."
The Seven Barrows trainer added: "We have had them come back from this. For his own sake he needs to be a good patient but he is at the moment."
Jess Stafford, from Thurloe Thoroughbreds - Buzz's owners, tweeted: "We are completely devastated and lost for words. Importantly, Buzz is on painkillers and is comfortable but the next 72 hours are very important.
"He's our absolute pride and joy. Thank you to his vet David Matheson and everyone for your kind messages. We will keep you updated."