Ruby Walsh will replace David Casey aboard Hedgehunter in the John Smith´s Grand National at Aintree on Saturday week.
The Willie Mullins-trained nine-year-old was partnered by Casey in race 12 months ago when he fell at the last but will now have Walsh, who won the race in 2000 aboard Papillon, on his back.
Walsh won the Irish National last Monday when prevailing on Numbersixvalverde, seeing off his father´s Jack High in the process.
Explaining the jockey switch, Mullins told the Racing Post: "Ruby is my stable jockey in Ireland and rides for Paul Nicholls in England.
"He was committed to ride Silver Birch at Aintree until he was ruled out of the race and he will now ride Hedgehunter for me.
"It is absolutely no reflection on David who is a top-class jockey. He will continue to ride on a regular basis for me but Ruby is my number one."
The news came as a further blow to Casey who was detained overnight at Blanchardstown Hospital in Dublin yesterday following a crashing fall from Emotional Article at Fairyhouse.