Trainer Paul Nicholls was dealt a huge double injury blow on Monday evening by the news Big Buck's and Al Ferof are set to miss the rest of the season.
The former was due to run in Saturday's Long Walk Hurdle at Ascot, while Al Ferof was being prepared for an assault at the King George VI Chase at Kempton on Boxing Day.
Nicholls told Betfair: "At evening stables, we discovered a problem with both Big Buck's and Al Ferof. I am not in a position to go into great detail at this point, but I can confirm that Big Buck's will not be taking up his engagement at Ascot on Saturday and Al Ferof will not be running in the King George."
Big Buck's' owner Andy Stewart said the remarkable nine-year-old, who has won his last 18 races, has suffered a leg injury and would not defend his crown in the Ladbrokes World Hurdle at the Cheltenham Festival next March.
He told Press Association Sport: "He didn't do it (sustain the injury) on the gallops. He was a little bit anxious in one of his legs at evening stables and after Clifford (Baker, Nicholls' head lad) and the vet inspected him, we decided to draw stumps. He'll not be running on Saturday and he won't be trying to win a fifth World Hurdle in March.
"I'm a little bit gutted, but no-one has died and the horse is perfectly well. When the horses come back in at the end of July we shall reassess the situation. If he hasn't got that zest and sparkle, he will be retired."
Al Ferof, a fine winner of the Paddy Power Gold Cup at Cheltenham in November, has damaged a tendon and will miss the rest of the season, said owner John Hales.
"We were all set for the King George, but things like this are part of the game. We don't know how he got the tendon injury, but that's him out for the season. We'll obviously get him reassessed by the vet, but you can bet your life the King George and then the Gold Cup will be the plan in 12 months' time.
"He's still a youngster and has age on his side."
Nicholls later tweeted neither Big Buck's nor Al Ferof had sustained career-threatening injuries and that they "both will be back".
28 February 2015Wayward back on right track
Investment gains Greatwood gold
Bal win delights connections
Glinger burns off Kelso rivals
Pipe proves he's a Soll man
Geraghty shines on Leave It
Walter back for another victory
Irish pair do battle in France
Geraghty: Sprinter will be fitter
Wylie lines up Cheltenham team
Twiston-Davies Blak in business
Divine Bishop on Festival trail
Irish duo set Doncaster poser
Night riding high for Grimthorpe
Glingerburn facing another battle
Pipe targets Aintree with veterans
Carlito primed for Kelso return
McCoy not planning Festival goodbye
Bridge camp praying for rain
Cook suspended from riding
27 February 2015Golantilla in Ballsbridge bid
Safety strikes in Zabeel Mile
Fehily confirms Zarkandar mount
Lieutenant bosses Purcell rivals
Dettori delights on Dubday
Many Clouds goes back to school
Maguire loses appeal
New One at ease for Faugheen clash
Foxrock still in Gold Cup picture
Apache ready to take flight in JLT
26 February 2015Higgins back in business
Cookie poised for April return
Silvi threat unsettles Riches camp
No going concerns at Cheltenham
Fry resigned to Fehily Ruby loss
Trip key to Balder success - King
McLernon gets nod for Holywell
Salsify leads Foxhunter field
Mullins unveils Bumper entry
Curtis hoping for Cross revival
Aurore misses Mares' date
25 February 2015Ton-up for in-form Pipe
Big display from George veteran
Credit to join the Premier league
Jack to duck Grimthorpe date
Tea preparing for National tilt
Geraghty rates Whisper World claims
George retains Module faith
Uramazin ready to go again
Coney team wait on Festival call
Aintree on Ceremony agenda
Silvi is all Gold - Nicholls
Bright Clouds gets serious
Puffin swoops at Leicester
Nicholls: Rheu call tough for Sam
Nicholls suffers Hinterland blow
Own on Cheltenham trail
BHA issues new anti-doping rules
Walsh hoping for a Champagne moment
That ruled out of World bid