Four-time Tour de France winner Chris Froome crashed as he made his way down the mountain following the 17th stage of this year's race when police mistook him for a fan.
Froome, wearing a black raincoat over his racing uniform, was returning to his team when there was a misunderstanding and police asked the rider to stop, causing him to come off his bike.
Earlier the Team Sky rider cracked on the final climb to Col du Portet, drastically decreasing his chances of a record-tying fifth title as he slipped to third on the overall standings.
The incident comes a day after police used tear gas to disperse a farmers' protest that had blocked the road with bales of hay.
Froome was among a large group of riders whose eyes needed treatment due to the tear gas.
Froome has been a repeated target of fans in this Tour after he was cleared of doping five days before the race began. He had been racing under the cloud of a potential ban for using twice the permitted level of salbutamol during his victory at the Spanish Vuelta in September.
He said he has been repeatedly spat at since the race started, and spectators have punched him and tried to make him fall off his bike.
Meanwhile US Anti-Doping Agency chief Travis Tygart said the management of Froome's salbutamol case was a fresh blow to the credibility of the World Anti-Doping Agency (WADA).
"Athletes should not be accused or it be inferred that they're not clean until proven through the established process and that didn't happen here - and he deserves the benefit of that presumption of innocence."
The UCI, cycling's world governing body, announced on July 2 the investigation had closed after working closely with WADA as no offence had been committed.
Tygart questioned the transparency of WADA's process in reaching its decision on the case and told BBC Sport once Froome's case became public knowledge all details of how he was cleared should have been released.
"You can never unring that bell and it's why more answers have to be provided, so that people have confidence that he's not just a star who got away with it - that's a natural conclusion."
A WADA spokesperson told BBC Sport Tygart's reckoning of the situation appeared to be "uninformed" and "unconstructive", adding: "In leading the fight against doping in sport, WADA is sometimes forced to make difficult decisions related to complex cases that people, who are not in possession of the facts, do not understand or agree with.
"This is one of those occasions. WADA is convinced that, in view of the complex and unique circumstances of Mr Froome's case, the UCI reached a correct and fair outcome."
