Robert Thornton has broken his arm in a fall at Hereford and is likely to miss the busy Christmas period.
The rider, 33, fell while riding Richard Lee-trained Western Whisky at the seventh fence in the totetrifecta Handicap Chase, bringing down Maraafeq in the process.
Maraafeq's rider Harry Challoner was unhurt, but clerk of the course Keith Ottesen confirmed Thornton's injury.
He was top jockey at the 2007 Cheltenham Festival, when his four victories included a triumph on Voy Por Ustedes in the Queen Mother Champion Chase.
The jockey is popular with punters because he is seen as an independent figure.
He refuses to be interviewed immediately after a race, saying the trainer and owner deserve to hear his opinion first.
When suffering with a knee injury in 2010, Thornton, a Liverpool fan, was offered help from Manchester United's medical team during his recovery.