Richard Johnson will ride Florida Pearl in the Tote Cheltenham Gold Cup.
Trainer Willie Mullins announced the move 24 hours after his stable jockey Ruby Walsh rode Commanche Court into second place in Kempton's Racing Post Chase.
That caused Commanche Court's Gold Cup price to plummet to 12/1 and Walsh's father, Ted, also trains the big race hope Rince Ri who could have a Gold Cup warm-up at Leopardstown next weekend.
Mullins said: "Florida Pearl's owner (Archie O'Leary) wanted a firm commitment that Ruby would ride his horse in the Gold Cup and Ruby couldn't give it to him. Ruby has a few irons in the fire so Richard Johnson will ride Florida Pearl in the Gold Cup."
Johnson took over from the sidelined Walsh in the Hennessy Gold Cup at Leopardstown and had the Mullins horse back in second when winning last year's Gold Cup on Looks Like Trouble.
Other significant jockey news centres on Kieran Kelly who will not ride the big SunAlliance hope Colonel Braxton at the festival. Kelly has ridden the John Magnier-owned horse in his starts this season but misses out on Cheltenham. A replacement has not yet been named.
Meanwhile, Ruby Walsh may have been edged out of big race glory at Kempton on Saturday but he returned to winning form with a vengeance at Naas.
The season's leading rider extended his lead by three winners and picked up a realistic Cheltenham contender into the bargain after Macs Gildoran ran out a neck winner of the Johnstown Novice Hurdle.
It was enough for Cashmans to cut Macs Gildoran's SunAlliance Hurdle price by five points to 20/1 but Willie Mullins was thinking even further ahead.
"It's great to see the faith I have in him justified. He's a dour stayer and if he takes to fences I think he will be a Gold Cup horse," claimed Mullins who is thinking again of allowing Saturday's Fairyhouse flop Be My Royal take his chance in the Bonusprint Stayers Hurdle.
"I think we'll let the hare sit for a few days with Be My Royal. It could be a case that that run was so bad it couldn't be true," he said.
Walsh hit the pockets of odds on backers after the 12/1 outsider Moscow Express was five lengths too good for the Arkle Trophy hope Knife Edge in the Newlands Chase.
"That's a surprise. The aim was to get around safely. Anything else was a bonus but Ruby and the horse get on great and Ruby did a great job," said Frances Crowley who had earlier seen Sackville confirm his SunAlliance Chase potential with a 2/9 success in the Nas Na Riogh Chase.
Michael O'Brien wasn't too disappointed with Knife Edge but admitted: "I expected him to pick up better. He seemed a bit sluggish but I wouldn't down him too much and he still goes for the Arkle."
Sackville remains a 5/1 chance for the SunAlliance even though he appeared to make hard work of beating just three opponents. David Casey's mount was less than fluent at some of the fences and had to be rousted along to beat River Clodagh by five lengths.
"He is very lazy and David was trying to give him as easy a race as possible," said Crowley.
Walsh's first winner was the Michael Hourigan-trained Just Our Job and Hourigan has a live Cheltenham contender in Mr Red Banner whose later victory in the three mile handicap earned him a 10/1 quote for the Coral Cup.
