Amateur jockey JT McNamara was airlifted to hospital in an induced coma after suffering serious injuries in a fall at the Cheltenham Festival on Thursday.
"I've been told JT is in an induced coma," his uncle, trainer Andrew McNamara, told the British Horse Racing Authority's website (www.britishhorseracing.com).
The 37-year-old Irish rider was treated by paramedics after his mount Galaxy Rock fell at the first fence in the Fulke Walwyn Kim Muir Challenge Cup.
Racing was delayed for 30 minutes before the jockey was flown to a Bristol hospital.
McNamara was conscious after the fall but had difficulty breathing, Irish Turf Club chief medical officer Dr Adrian McGoldrick said.
"It's a dangerous sport and it's a sight you see that unfortunately crops up," 17-times champion jockey AP McCoy told the BBC.
"We're very lucky we have excellent medical care. We just hope he's going to be OK."
Matuhi also sustained a serious spinal injury and was put down after the horse fell at the last fence in the Byrne Group Plate.