Ruby Walsh suffered a broken leg in a fall from Let's Dance at Punchestown on Saturday.
Walsh's mount was sent off the 4-9 favourite in the Frontline Security Grabel Mares Hurdle, but came to grief four out.
The rider - who had two falls earlier on the card - was attended to on the track before being taken to hospital in Naas for X-rays.
Walsh told Racing UK: "I've suffered a fracture of my right tibia.
"I'm going to Tallaght Hospital now to see a specialist and I'll know a lot more tomorrow."
With the jumps season hitting top gear, Walsh was due to partner the long-absent former Champion Hurdle hero Faugheen in the Morgiana Hurdle at Punchestown on Sunday.
Walsh's close friend and former rival Sir Anthony McCoy told ITV Racing: "He's heartbroken, I've been texting him and he's been texting me back. He's missing a ride like Faugheen tomorrow.
"He's had a few bad falls in the past. He's the best jockey I've ever seen and tougher than anyone I've ever seen.
"He's very low at the moment, but in a few days and a few weeks he'll be trying to get himself back. He'll get through it.
"It's a big loss to National Hunt racing to see him not riding and Willie Mullins is going to miss him, but he'll be back."
The Turf Club's chief medical officer Dr Adrian McGoldrick said following the fall: "Ruby has a probable fracture of his right tibia and fibia.
"He is going to Naas for X-rays and then he'll be transferred to Tallaght.
"He got a nasty kick off his own horse when he was trying to get up. He's fully alert, though."