Jockey Brian Toomey is in hospital with a life-threatening head injury after suffering a heavy fall during a race.
The 24-year-old Irish rider was partnering Solway Dandy at Perth when the horse fell three flights from home.
Toomey is attached to the yard of North Yorkshire trainer Kevin Ryan and is the boyfriend of Ryan's daughter, Amy.
Champion jockey AP McCoy was among the figures from the racing world to send their best wishes, tweeting: "Thoughts and prayers are with Brian Toomey."
The dangers of jump racing
- Jump racing is a risky sport - with jockeys braced for a fall on an estimated average of one in 16 rides
- Popular amateur jockey JT McNamara was paralysed after suffering spinal injuries in a fall at the Cheltenham Festival in March
- Peter Toole was another jockey to be badly hurt - although he has recovered from a serious head injury at Aintree in April 2011
- The Injured Jockeys' Fund helps the families of riders, and is supporting the loved ones of Brian Toomey
McCoy, who has won the title 18 times, added: "Let's hope he will be OK."
Speaking shortly before 22:00 BST on Thursday, a spokesman for NHS Tayside said Toomey was "suffering from a life-threatening head injury".
Amy Ryan, last season's champion apprentice rider, travelled from a meeting at Haydock, Merseyside, to the hospital in Scotland. The jockey's family is expected to visit him on Friday.
His fall happened during the Perth Festival Conditional Jockeys' Handicap Hurdle.
An air ambulance arrived shortly after the accident, which happened in the 17:00 race, but Toomey was transported to Dundee's Ninewells Hospital by road.
Toomey has ridden 49 winners over the jumps since 2008 and has represented Ryan's stable at the Cheltenham, Aintree and Punchestown festivals.
He has three victories from 24 rides in the 2013-14 National Hunt season, including Whiskey Ridge for Grand National-winning trainer Sue Smith at Wetherby on 30 May.
Many of his weighing room colleagues have been sending their best wishes, including Thomas Messenger, who tweeted: "Praying for good news on Toomey today. Thoughts are with Amy and his family. It's a terrible game at times."
Paddy Brennan, who won the Cheltenham Gold Cup in 2010 on Imperial Commander, said: "Praying for Brian Toomey this morning. Thoughts with his family and Amy."