Richard Johnson has ridden Warren Greatrex's star mare on each of her eight starts over fences to date, a run which has yielded four victories, including a Grade One triumph at last year's Dublin Racing Festival in the Flogas Novice Chase.
The nine-year-old is all set to head to Ireland for Sunday's 250,000 euros feature, but with the British champion jockey sidelined by injury, connections require a new pilot.
Greatrex told the PA news agency: "After speaking to the owners, we decided to go with an Irish-based jockey who knows the track at Leopardstown really well - and we've decided Mark Walsh is the man for the job.
"She (La Bague Au Roi) is in great form at home and I couldn't be any happier with her. The plan is to leave on Friday morning, to then give her the chance to get settled in. Hopefully we'll see a big run from her."
La Bague Au Roi is a best-priced 33/1 for the Irish Gold Cup, with Kemboy and Delta Work disputing favouritism.
Next in the betting is Presenting Percy, who made a promising start to his campaign when third in the John Durkan at Punchestown, but could finish only fifth in last month's Savills Chase - a race won by Delta Work, with Kemboy fourth.
Presenting Percy's rider, Davy Russell, said: "He seemed to run a very good race in the John Durkan and we were hoping for a bit of improvement going to Leopardstown.
"He ran really well (in the Savills Chase), but I just felt from the back of the last to the line he might stay on a bit better.
"We're hoping for improvement from that run, but he'll need it because it's a very competitive sphere. I'm looking forward to having another go at them. He's a very talented horse."
