The Arkle Trophy winner could instead reappear at Leopardstown’s Christmas Festival.
The seven-year-old is unbeaten in his completed starts over fences, his only reverse being when he fell at Thurles on his chasing debut.
Mullins tweeted: “Unfortunately UnDeSceaux will not run this weekend. He has been a little flat in himself the last two days.”
Mullins said that he will now “probably” look to run Un De Sceaux at Leopardstown on December 27, where he holds an entry in the Paddy Power Dial-A-Bet Chase.
The absence of Mullins’ gelding, who was reported to have thrilled connections when schooling after racing at Thurles last week, has left the Paul Nicholls-trained Vibrato Valtat as the 7-4 favourite with the sponsors.
Next best at 4-1 is Nicky Henderson’s resurgent grey Simonsig, winner of the 2013 Arkle but only seen once since, when pleasing behind stablemate Bobs Worth over hurdles at Aintree last month.
The Seven Barrows handler can also call on Josses Hill, although he is likely to wait for the Peterborough Chase at Huntingdon 24 hours later.
Henderson said: “It’s not changed our plans, the plan is still to run Simonsig on Saturday and Josses Hill on Sunday, but I’ll talk to the owners and just see.
“Nothing much has changed in terms of the race, Special Tiara wants a good gallop and Simonsig wants to settle down a bit.
“It’s dried up a bit down there according to the latest going report, he wants nice ground, they all do.
“I’m happy with him, I wouldn’t want to be going into a Grade One if I wasn’t.”
Nina Carberry, meanwhile, will partner Somersby for the first time in the weekend feature.
Trainer Mick Channon has again turned to the leading Irish amateur after the partnership were successful when Knock House won a race at Cheltenham in November.
Channon said: “We’ll be going to Sandown for the Tingle Creek and Nina rides, which is great news.”
Somersby, last season’s Queen Mother Champion Chase runner-up, is an old hand around Sandown, having finished second in the last two renewals of the Tingle Creek.
The 11-year-old showed at Cheltenham last month that the fires still burn brightly when he finished second in the Shloer Chase behind a revitalised Sprinter Sacre and will appeal to each-way punters.
Meanwhile Noel Meade is aiming Waxies Dargle at The Ladbroke at Ascot on December 19.
Following a fine run in the Greatwood Hurdle at Cheltenham where he finished third to Old Guard, he has been installed as 12-1 second favourite by the sponsors.
“All is well with Waxies Dargle. He came back from Cheltenham OK and the plan is to run in The Ladbroke at Ascot,” said Meade.
“We were happy enough with his run in Cheltenham. We would obviously have been happier had he won but it looks a good run on paper.
“The softer the ground, the better his chance will be at Ascot.”
Along with Waxies Dargle, the Irish challenge looks strong with Gordon Elliott, who has won two of the last three renewals with Cause Of Causes and Bayan, entering Diamond King, Vercingetorix and Hostile Fire.
Willie Mullins could run Noble Inn, Renneti or Sempre Medici with Sort It Out and Princely Conn also in the mix for Ireland.
Following two big handicap successes already this season with Annacotty and Smad Place, Alan King has the 10-1 favourite in Winner Massagot.
James Ewart’s Aristo Du Plessis has been given an entry as he continues to improve.