JT McNamara has undergone surgery on the serious neck injury he sustained in a fall at Cheltenham on Thursday.
The 37-year-old was injured in a first fence fall from Galaxy Rock in the Fulke Walwyn Kim Muir Challenge Cup.
McNamara, one of the leading amateurs on the circuit for a number of years, was airlifted to hospital after being treated by the on-course medics.
Conscious following the fall according to officials at the track, he was put in an induced coma before his transfer to Frenchay Hospital in Bristol.
Dr Adrian McGoldrick, chief medical officer for the Irish Turf Club, reports there to be no change in McNamara's condition but confirmed the rider has damaged two vertebrae.
"We can confirm that amateur rider J T McNamara suffered two fractured vertebrae in his neck yesterday," he said.
"He is currently in theatre in Frenchay Hospital, Bristol. There will be no further news until tomorrow and we will keep everyone informed, His wife Caroline is with him."
McNamara has a long-standing association with owner JP McManus, having ridden many winners in the famous green and gold silks over the years on horses like Spot Thedifference.
McManus, speaking after seeing his At Fishers Cross win the Albert Bartlett under Tony McCoy, said: "We're all thinking of JT and what he's going through, we feel guilty being here today, we feel we should be doing something for him.
"All our prayers are with him and hopefully they will be answered. Those jockeys, they give us so much - they give us so much pleasure, as everybody does in the game. We should be so thankful to them all.
"To Caroline and her family, we are thinking of you all. He will remain in our thoughts and in our prayers."
McCoy said: "It's very hard to be happy on a day like today with what happened to John Thomas McNamara. You've got to enjoy these moments.
"I'm very pleased to ride a winner for JP as he was in tears last night over what had happened to John Thomas."