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 has battled back from injuries in the past and even rode a winner, Voy Por Ustedes, when he had a broken collarbone during the 2006 festive period.
When suffering with a knee injury in 2010, Thornton, a Liverpool fan, was offered help from Manchester United's medical team during his recovery.