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".
30 June 2015Time makes all the right moves
Canadian dream for Odeliz
Ground to dictate plans for Ribbons
Walsh remembers 'heavyweight' Kauto
Queen possible for Godolphin debut
Towcester chief facing BHA charges
Intilaaq in line for return
Down Royal proud to have seen Kauto
McCoy salutes 'amazing' Kauto
Nicholls leads Kauto tributes
Nicholls leads Kauto tributes
Sad end for super Star
Star put down after paddock fall
Doyle keen on Beau chance
Pontefract firsts for Hannon
Horn long odds-on for Eclipse
Frustration continues for Tudhope
Globetrotting Glance retired
Package heads for retirement
Falmouth caution for Integral
Stars on Leger course
Chase set for drop in class
Vintage option for Sails
29 June 2015France for Force
Karpino King George plans on hold
Firecrown out for compensation
Prat possible for Estidhkaar
Lowther in Lady's sights
Bay bypasses Eclipse date
Beach life suits red-hot Heffernan
Forever foxes sprint rivals
Diamond sparkles in Pretty Polly
Treve too good at Saint-Cloud
Aquam impresses on debut
Pilot leaves rivals toiling
Kodi has Jean Prat option
Aeolus given French targets
Ervedya to face her elders
28 June 2015Aquam impresses on debut
Aktabantay in Jean Prat mix
Believe seeking redemption
'Positive' signs for Creighton
Law ready to Rock at the Curragh
Jack's the lad for Curragh glory
Hughes reveals training ambition
O'Neill continues in fine form
Cliffs on track in Railway
Nicholls' Debt takes Celebration
Fab four for Doyle
Byron back with a bang
Quest for Plate ends in victory
Aeolus in Chipchase surprise
27 June 2015Markaz makes his mark
Diamond sparkles in Empress
Choir hits right note at Newmarket
Cookie out of Plate
Strong British raid on Pretty Polly
Lancaster aim for Mustadeem
Creighton in induced coma
Winston hoping for swift return
Grant recovering after Curragh fall
Winston taken to hospital
O'Brien pleased with Curragh ground
Buratino on path to Phoenix
Combat primed for Criterion
Wachman hopes to be sitting Pretty
Treve all set to star on Sunday
Danzeno defends Chipchase crown
Hopeful Niven to check Plate ground
Island out for Railway success