The 10-year-old has looked as good as ever in winning his two starts this season and connections remain keen to test the multiple Grade One winner over three miles on a sound surface.
However, with conditions likely to be testing at Kempton next week, Sizing Europe is set to instead head to Leopardstown for either the two-mile-one-furlong Paddy Power Dial-A-Bet Chase or the Lexus Chase over three miles.
With rain continuing to fall over most of Britain and Ireland, it would seem the shorter race is his most likely target.
De Bromhead said: “We said at the start of the season we’d love to try him over three miles on better ground, but it doesn’t look like we’re going to get that at the moment.
“Sometimes you do at Kempton on Boxing Day, but unfortunately we won’t this year.
“He has the two options at Leopardstown and we’ll leave him in both races , but the way the weather is going at the moment, I would imagine he’ll probably run in the two-mile race.”
Another Irish-trained horse ruled out of the Boxing Day feature is First Lieutenant.
Mouse Morris scratched his Hennessy Gold Cup third from the Kempton Grade One on Wednesday and he will instead head for the Lexus on December 28.
Morris plans to saddle China Rock in the same race, his first appearance since claiming the Punchestown Gold Cup in the spring.
“He’s in great form, but we’ve decided to stay at home with him,” said the trainer.
“Leopardstown will be as good a ground as we’ll get over Christmas, so we’ll go there and see what happens. China (Rock) will be there as well. I’m very happy with him at the moment.”
Fifteen horses remain in the King George following the latest confirmation stage.
They are headed by the Nicky Henderson-trained Long Run, second to Kauto Star 12 months ago, but the winner at a rescheduled renewal the previous season.
Stable companion Riverside Theatre, runner-up to Long Run that day, has also stood his ground, while Henderson also has the 2012 Champion Chase victor Finian’s Rainbow.
Philip Hobbs is represented by last season’s third Captain Chris, Menorah and Wishfull Thinking.
David Pipe has supplemented Rehearsal Chase winner Junior and has left in Grands Crus, who would be having his first run since undergoing a wind operation.
Colin Tizzard has a leading contender in Cue Card, while David Bridgwater’s Cheltenham Gold Cup runner-up The Giant Bolster and Martin Keighley’s Champion Court also feature.
Kauto Stone, half-brother to five-times King George hero Kauto Star, is Paul Nicholls’ only entry after the defections of the injured Al Ferof and the ill-fated Cristal Bonus.
Sir Des Champs, from Willie Mullins’ stable, is the only Irish-trained possible.
Hunt Ball and For Non Stop complete the list of possible runners.
Meanwhile Hurricane Fly is one of eight remaining entries for the Istabraq Festival Hurdle at Leopardstown on December 29.
The 2011 Champion Hurdle hero lost his Cheltenham crown when beaten into third at Prestbury Park in March, but did sign off the season with victory at Punchestown and made a winning return at the same track in November’s Morgiana Hurdle.
The eight-year-old is one of three entries for Willie Mullins, with Thousand Stars and Zaidpour also in the mix for the two-mile Grade One.
John Quinn’s hugely impressive Fighting Fifth hero Countrywide Flame is the sole British-trained contender, while Captain Cee Bee, Monksland, Tilabay and top-class mare Unaccompanied complete the field.
Harry Fry is adamant Rock On Ruby can reverse the form from Saturday’s International Hurdle back at Cheltenham in March.
The Seaborough handler was delighted with his stable star’s effort to take third place behind Zarkandar and Grandouet on his first run of the season in soft ground.
He is looking to give last season’s Champion Hurdle hero one more run ahead of the defence of his title.
“He travelled down the hill like the best horse in the race – he had Zarkandar off the bridle at the top of the hill – and just turning in he got caught out with the lack of a recent run which you need to have at that sort of level on that ground,” Fry said in his blog for StanJames.com.
“He’s had two wind operations and those conditions are going to find out any weaknesses whether they’ve been fixed or not.
“What it turned into was a real stamina test so, on better ground, we’ve very confident about his chances come March.
“The 12-1 he went out to was massive and we snapped it up as quickly as we could.
“What Saturday showed you was a real staying performance from Zarkandar which may have proved he was less like a Champion Hurdle horse.
“Grandouet obviously travelled well and had his turn of foot blunted by the conditions.
“He’s the one to fear come March because that was a great run off a 12-month lay-off and his turn of speed will come into play on better ground.”