French Europcar rider Thomas Voeckler was struck by a car and appeared to injure his shoulder just before the start of the Tour du Limousin in Limoges on Tuesday.
Voeckler, 35, was preparing for the start of the first stage of the four-stage race when he was hit by the car at a roundabout, an AFP correspondent at the scene, who witnessed the incident, said.
He appeared to have hurt his left shoulder and was taken to hospital in Limoges for tests, with the official Twitter feed of the race revealing he would not take part and had a suspected broken collarbone.
Voeckler, who has won four stages on the Tour de France and was King of the Mountains in 2012, could now struggle to make the road World Championships, which will be held in Ponferrada, northern Spain, in late September.