Jockey Chelsea Jokic has a suspected fractured skull after a fall in a jump-out in Mackay in northern Queensland.
Jokic is in Mackay Hospital awaiting further tests and is likely to be transferred to either Brisbane or Townsville.
Queensland Racing Integrity commissioner Ross Barnett said the 21-year-old was riding an unraced horse in the jump-out at Mackay following Thursday's race meeting.
"Stewards reported the horse appeared to blunder when released from the barrier and Ms Jokic fell," Barnett said.
"Ms Jokic was immediately treated on the track and then taken by ambulance to the Mackay Hospital."
Barnett said stewards would open an inquiry when Jokic was well enough to attend.
Jokic is now based in south-east Queensland with her trainer-brother Michael Jokic but travels around the state for rides.
She as ridden 46 winners this season.