British rider Mark Cavendish suffered concussion and a whiplash injury following a crash which forced him to pull out of the Abu Dhabi Tour during the neutral zone on stage one.
The Manxman, who won the opening stage of last year's race, hit the deck shortly after setting off from Madinat Zayed.
The 32-year-old got back on his bike, but was forced to abandon soon after.
Cavendish's team Dimension Data confirmed in a post on their official Twitter feed that the British rider had fallen "on the same shoulder he broke last year" following a crash with Peter Sagan on stage four of the Tour de France.
A later medical update from team doctor Adrian Rotunno did not mention the shoulder and said there were no signs of a serious neck injury.
"Mark sustained a concussion and a whiplash injury after his crash today. Due to the concussion, we were not willing to risk rider safety and the call was made for Mark to stop the race," Rotunno said in a statement posted on their official website.
"A serious neck injury has been excluded in hospital. He currently has some concussive symptoms and neck pain, but is otherwise stable. We will monitor Mark's condition closely going forward."
Wednesday's crash happened ahead of the official start of the 189km opening stage between Madinat Zaya and Adnoc School.
Television replays showed the incident appeared to have been caused when the race director's car slowed down in front of the peloton, which resulted in a groups of riders behind having to brake sharply, with several then falling down.