Alitor is an imposing challenge in his way but a remarkable Grade One four-timer still looks to be in Un De Sceaux’s sights at Ascot on Saturday.
Willie Mullins' star is one of just a quartet of entries left in the Matchbook Clarence House Chase after Monday's entry stage.
Un De Sceaux completed three-in-a-row in the extended two mile event last year.
The Mullins stalwart looks set to provide the main challenge to Altior who was immediately installed a 1-4 favourite to maintain his unbeaten record over jumps.
Mullins indicated on Monday he will be keeping a close eye on ground conditions at Ascot. They are currently reported as good and good to soft in places.
That could favour Altior who defeated his Irish rival in last month’s Tingle Creek Chase at Sandown on much softer conditions.
However, Un De Sceaux is unbeaten at Ascot and a fourth win at the weekend would rank with some of National Hunt racing’s great winning streaks.
Kauto Star completed four in a row in the King George VI Chase between 2006 and 2009 before winning the race again in 2011. Big Bucks also completed four in a row in the Stayers Hurdle at Cheltenham from 2009 to 2012.
Another Mullins star, Quevega, holds the Cheltenham festival record with six in a row in the OLBG Mares Hurdle between 2009 and 2014. However that was before the race was promoted to Grade One status.
The other two horses left in Saturday’s race are Fox Norton and Diego Du Charmil.
Mullins has had to rule out his Royal Bond winner Quick Grabim from the Cheltenham festival in March.
Quick Grabimn had been 14-1 for the opening race of the festival, the Supreme Novices Hurdle, but Mullins reported: “He has had a setback and will not make Cheltenham. He suffered a stress fracture after his last run but hopefully he will make it back in time for Punchestown. He’ll get all the time he needs.”
The champion trainer has won the Goffs Thyestes Chase six times already and has 15 entries left in next week’s historic race at his local course in Gowran Park. They include the Cheltenham Gold Cup entries Total Recall and Invitation Only.
Last year's winner Monbeg Notorious is one of ten Gordon Elliott entries for the race. A total of 46 horses in all are left with Ramses De Teillee one of two for cross-channel trainer David Pipe.