Britain's Mark Cavendish pulled out of the Abu Dhabi Tour during stage one after falling onto the same shoulder he broke in last year's Tour de France.
The former world champion collided with a vehicle that had braked suddenly before reaching the start line in the western desert of Madinat Zayed, according to the official Abu Dhabi television channel.
Today's crash happened after the race director's auto looked to slow down suddenly as the following riders braked to avoid colliding with it.
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Race leader Alexander Kristoff was among those caught out by the echelons in the peloton, leading to the Norwegian's UAE Team Emirates having to help chase the lead group. He now has some concussive symptoms and neck pain but is otherwise stable.
The Brit, 32, was in the neutral zone at the start of the opening stage when he was involved in a pile-up.
It says he fell on the shoulder which he broke previous year, suffering whiplash and a concussion in the process.
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The unfortunate result was that Cavendish had to abandon the Abu Dhabi Tour as a result of the crash.
The team weren't willing to allow Cavendish to continue due to the concussion, and will continue to monitor his condition.
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