Jonbon has been ruled out of today's Champion Chase at Cheltenham due to concerns over the health of trainer Nicky Henderson's travelling contingent to the Cotswolds course.
Henderson has made the decision to pull his much-fancied horse out of the main race of the second day of this year's Festival as a result of analysing how his charges raced on Tuesday's opening day.
The Seven Barrows trainer said that there was "something affecting nearly all our horses" during Tuesday's racing, and added that while it was a tough decision to withdraw Jonbon, it was one made in the best interests of the horse.
First Street and Kingston Pride have also been withdrawn and Henderson expects further non-runners throughout the remaining days of this year's Festival.
In a subsequent statement he confirmed Shishkin will not run in Friday's Gold Cup after showing "an unsatisfactory picture". Champ is also out of Thursday's Stayers' Hurdle.
Henderson posted on X, formerly Twitter: "Very sadly it will not be possible for Shishkin to run in the Gold Cup on Friday. He was scoped as have all our potential runners this week, but unfortunately he has shown an unsatisfactory picture on which he couldn't possibly run.
"He appears to be 100% in himself and has been working and schooling better than ever and we were really looking forward to Friday, it is hoped that along with all the other non-participants this week that they will be back in time for Aintree or Punchestown.
"Regrettably Champ has also succumbed and will not run in tomorrow’s Paddy Power Stayers’ Hurdle and the equivalent race at Aintree could be on the agenda."
Shishkin was the only horse from the five-day stage not declared, meaning Galopin Des Champs will face 11 rivals in his bid to land back-to-back Gold Cups and emulate a former stablemate in Al Boum Photo.
Henderson went into the Festival under a cloud following the withdrawal of Champion Hurdle title holder Constitution Hill and a disappointing run of form from his stable as a whole.
Luccia provided Henderson with a boost when finishing third behind State Man in the Champion Hurdle, but his other five runners on Tuesday were all pulled up.
"I'm afraid we've had to make some very tough decisions following the very disappointing performances of all bar one of our horses yesterday," read a statement released on Henderson's social media.
"It was there for all to see that there's obviously something affecting nearly all our horses and consequently we have reluctantly decided that Jonbon, First Street and Kingston Pride will not run today.
"It's impossible to identify any reason for all the disappointments and none of these three horses have given us any cause for concern and all yesterday's runners were scoped clean post-race and I'm glad to say all are sound this morning. There will unfortunately be further non-runners on Thursday and Friday.
"I hope everybody will appreciate that we have to do this in everybody's interests, particularly the horses. It is very, very disappointing for everybody."
Among Henderson's high-profile entries for the rest of the week is JCB Triumph Hurdle favourite Sir Gino.
Regarding Sir Gino Henderson said: "Sir Gino, at the moment, is a definite intended runner.
"There were rumours flying around last week that something was amiss, but there’s nothing wrong with him at all at the moment. But a day is a long time with these horses.
"He was great this morning, his blood and everything is good and all being well he’ll be here."
Additional reporting: PA
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