Dougie Costello has come in for the plum spare ride on Lord Windermere in the Hennessy Gold Cup at Newbury on Saturday due to an injury to Robbie McNamara.
The leading Irish amateur broke his collarbone schooling for Dermot Weld on Friday morning and trainer Jim Culloty has snapped up Costello to partner last season's RSA Chase winner in the prestigious staying handicap chase.
"I'm thrilled. He's got a serious chance and I'm over the moon to be asked," said Costello.
"I've seen him plenty and I'll watch a few more replays of his runs tonight again and I'll speak to Jim and Robbie.
"It's a shame on Robbie's part. It was such a good ride and just one of those things. It's a great spare for me to pick up."
Culloty said: "Dougie's a good rider. It's not ideal having to change at the last minute but these things happen. Lord Winderwere is in great form."
Lord Windermere has been well-supported this week as he tries to emulate Bobs Worth by winning both the RSA Chase and Hennessy in the same year.
"He's done plenty and is as fit as I can get him. He did a blinding piece of work last week at the Curragh and I couldn't be happier with him," the County Cork handler told At The Races.
"Obviously going into a race like that I'd have loved to have had a run under his belt, but that's not the case. It's ground conditions really as much as anything in Ireland. It's been a lot drier in Ireland than it has in England.
"He's a year older and he is the exact same weight as he was for his first time out last year.
"He's promised to be a horse better over a longer trip. We started him off over two miles as he'd got form at that trip over hurdles and we gradually stepped him up.
"But last season in Ireland, the ground was absolutely bottomless the whole year basically so that's why I didn't step him up three miles earlier.
"Saturday's race will be furthest than he's ever gone in his life, but I'm not worried about that really.
"I think we are going there with a very good chance. I'd be far more confident had we had a run under our belt, but that's how it is."