Sire De Grugy will not defend his Tingle Creek crown.
And his chances of retaining the Queen Mother Champion Chase title at the Cheltenham Festival in March have also been cast into doubt after he was diagnosed with a hip injury.
The eight-year-old son of My Risk, who hails from the West Sussex yard of Fontwell favourite Gary Moore, was withdrawn from the Shloer Chase on Sunday after he was found to be lame.
A bone scan of the two-mile chasing star, who claimed four Grade 1 wins last term, highlighted a hip problem.
Moore is unable to put a timeframe on his talent’s recovery but has already ruled out a return to Sandown for the Tingle Creek next month.
The Lower Beeding trainer hopes to have Sire De Grugy, whose stable-mate Seven Woods suffered a narrow defeat in the Southern National at Fontwell on Sunday, back for the Festival in the spring.
But there are no guarantees he will make the Prestbury Park meeting.
Moore, who initially feared a broken bone, said: ‘He has not fractured his pelvis or suffered a stress fracture but he does have a hot area in his hip.
‘He’s done some damage to his hip and I don’t know if that’s good or bad really.
‘What happens now is he will spend the next month on the walker and then he will be rescanned.
‘It’s not the worst case scenario but it’s hard to tell the extent of the damage.
‘We’ve never had anything like this happen before.
‘He definitely won’t be running in the Tingle Creek, though, and he won’t run again this year.
‘I’m hoping Cheltenham is not ruled out – the Champion Chase now has to be his target.
‘I don’t think this will be season-ending. I don’t really know but I certainly hope not.’
Sire De Grugy finished second to Kid Cassidy in the Shloer Chase at Cheltenham 12 months ago before embarking on a run of five consecutive wins.
He followed Tingle Creek glory with a Grade 2 Desert Orchid Chase success at Kempton and then rattled off three more wins at the top level – in the Clarence House Chase, the Champion Chase and Celebration Chase.
The French-bred gelding’s form saw him rise to a rating of 172 and crowned king of the two-mile chasers.
Meanwhile, Sire De Grugy’s stable-mate Seven Woods delivered the finest display of his career only to go down by less than a length to Gorgehous Lliege in the Southern National at Fontwell on Sunday.
The eight-year-old son of Milan was unable to take advantage of his rival’s slip two fences from home – making a mistake of his own – before getting beaten in the final 75 yards.
Gorgehous Lliege was steered home by Arundel jockey Liam Treadwell at 8/1, with Incentivise a distant third.
Elsewhere on the card, jockey Daryl Jacob and trainer Colin Tizzard linked up for a double. Wizards Bridge won the toteexacta Pick The 1-2 Maiden Hurdle at 13/8 and Kings Lad took the John Rogerson Memorial Novices’ Limited Handicap Chase at 9/2.
Bredon Hill Lad kicked the meeting off with an even-money success in the Win Big With The totejackpot Novices’ Handicap Hurdle and Beau Lake won the totepool Racing’s Biggest Supporter Salmon Spray Handicap Hurdle.
Southway Star was the easy winner of the totepool Bet On All UK Racing Handicap Chase – justifying his place as 4/11 favourite.
And the final race – the totetrifecta Pick The 1-2-3 Handicap Hurdle – went to Zero Visibility at 4/1.