The seven-year-old won the January 2011 race and was runner-up on Boxing Day last year to Kauto Star, who was retired in October and has now embarked on a career in dressage.
However, champion trainer Paul Nicholls has entered Kauto Star's half-brother Kauto Stone for Wednesday's showpiece.
Captain Chris Champion Court Cue Card For Non Stop Grands Crus Junior Kauto Stone Long Run Riverside Theatre The Giant Bolster The race is likely to go ahead despite the wet weather hitting other meetings.Clerk of the course Barney Clifford has described the ground as heavy, but perfectly raceable.
Meanwhile, David Pipe saddles two contenders in Grands Crus and Junior at Kempton Park.
Trainer Nicky Henderson has a second horse, Riverside Theatre, in the race, while Philip Hobbs's hopes rest on Captain Chris, who finished third last year, after withdrawing Menorah and Wishfull Thinking at Sunday's final declaration stage.
The field is completed by Champion Court, For Non Stop, Cue Card and last season's Cheltenham Gold Cup runner-up The Giant Bolster, who will be ridden by Tony McCoy.
The other horses withdrawn on Sunday were Hunt Ball, Sir Des Champs and Finian's Rainbow, while Sizing Europe was ruled out on Thursday.
Long Run's owner Robert Waley-Cohen hopes his horse, the bookmakers' favourite, can improve on last month's defeat by Silviniaco Conti in the Betfair Chase at Haydock.
"The race wasn't run to suit at Haydock and the ground was quite tricky for a horse that isn't used to running on that sort of heavy ground," explained Waley-Cohen.
"It's possible the Gold Cup he won as a six-year-old might have taken a hell of a lot out of him, it might be that Kauto Star was a hell of a good horse last year.
"He had a quiet week after Haydock but he's in good order and we hope to have him cherry-ripe for Kempton."
