Jockey Frederik Tylicki has been told by doctors he has a T7 paralysis - meaning he has movement in the upper half of his body but not lower - after he sustained spinal injuries in a fall at Kempton on Monday.
The Injured Jockeys Fund announced the news in a statement on Friday evening.
Tylicki was admitted to the major trauma unit at St George's Hospital in Tooting - where he remains in intensive care - after he fell from the David Elsworth-trained Nellie Deen in a four-horse melee that led to the abandonment of the meeting.
Lisa Hancock, CEO of the IJF, said: "After his fall at Kempton Park Racecourse earlier this week, Freddy Tylicki was transferred to St George's Hospital in London, where he has since undergone surgery to his spine.
"His surgical team have confirmed that Freddy has a T7 paralysis, which means he has movement in the upper half of his body but not his lower.
"Freddy remains in intensive care and is not receiving any visitors for the foreseeable future.
"His family would like to thank the St George's staff for the care he has received. As this is a very difficult time for Freddy and his family, they would like to thank everyone for their good wishes, and for continuing to respect their privacy."
Tylicki was airlifted to hospital when Nellie Deen and her rider both fell halfway through a one-mile maiden for fillies.
Jim Crowley, who was riding Electrify, was consequently brought down, but the newly-crowned champion jockey, who was taken by road ambulance to hospital, escaped from the pile-up with a broken nose and was released that evening.
Steve Drowne avoided injury when his mount, Skara Mae, was also brought down, while Ted Durcan was unseated from Sovrano Dolce and suffered a broken ankle.
Reacting to the news, Drowne, who is joint-president of the Professional Jockeys Association, said: "It just shakes you. Obviously being there the other day you could kind of guess it was pretty serious, but you always hope and think it will be OK. The news seemed a bit positive for a while, but it is just sickening.
"I've never known a mood like that in the weighing room. It has certainly shaken us, it could have been anyone of us.
"He is everyone's friend and he loved doing what he was doing and had just had his best year ever, getting a couple of Group Ones in the book. But racing is probably the last thing he is thinking about now."
He added: "It is terrible and really makes you feel sick. Monday was not a good day and it really brings it home, what can happen to any of us.
"I can't ever remember him being down. We all go through the doldrums a bit, but he was never like that - he was always so positive."
Tylicki had this year been an emerging force in the weighing room, having claimed a first Group One victory aboard Speedy Boarding at Deauville in August.
He then secured a second top-level Flat triumph when the same filly won the Prix de l'Opera on Arc weekend at Chantilly in October.
Tylicki was named champion apprentice jockey in 2009 and counted the John Smith's Cup at York amongst his other previous big-race victories.