Jamie Moore faces a lengthy spell out of action after breaking his back and sternum in a fall at Fontwell.
The jump jockey took a crashing tumble from Alka Step at the fifth-last fence in Tuesday's attheraces.com Novices' Handicap Chase.
Moore, 35, received treatment on track and was taken to Brighton Hospital for X-rays and further assessment.
His father, West Sussex trainer Gary Moore, said: "He's fractured his back and also his sternum.
"He'll be off for a while. We don't know anything more at the moment.
"They are waiting to see if they are going to operate or not. We're not quite sure yet."
