French star Thomas Voeckler broke his collar bone when he crashed into a car during training on Wednesday and is out of the Tour Down Under, race organisers said.
The 34-year-old was taken to a sports clinic for X-rays immediately after the accident, which happened on a ride near the Adelaide beach suburb of Glenelg just hours after his arrival with his Europcar team.
"He will fly out of Adelaide tomorrow afternoon to return to Nantes in France for treatment," organisers said in a statement.
Voeckler said it was the first time in his career he had hit a car in training.
"When we go to train this morning a pedestrian crossed the road so a car braked very quickly and I didn't have time to brake and I bumped into the car," he said.
"I immediately understood that my collar bone is broken as it's the third time it's broken."
He fractured the same collar bone for the first time in 2009 in the Paris-Nice event and again in a crash during the Amstel Gold Race last April.
Voeckler had an operation earlier this month to remove the metal plate that was put in after that crash.
"It's been 12 days that the other plate was off and it was okay but I must not crash on it," said Voeckler, who has been a professional for more than a decade.
"There was a small risk and it's the first time in my career... that I hit a car in training... that's the way it is, it's a pity."
A winner of four stages and the 2012 mountains jersey at the Tour de France, Voeckler said he was looking forward to his first appearance in the six-stage Tour Down Under, which starts on Sunday.
"I was really happy to spend two weeks here even if my shape is not 100 percent," Voeckler said.
"When I am racing somewhere I always try to attack or take a breakaway that was my goal this time and to train for the other racing of the season (but) now I have to take time to get better and we'll see step by step."
His climbing abilities were expected to make him well suited to the 2014 route around the South Australia capital.
Race director Mike Turtur has described Voeckler as "an icon of the sport" and voiced disappointment on Wednesday.
Team Europcar manager Andy Flickinger said Voeckler would not be replaced and the starting line up would be the remaining six riders Yukiya Arashiro, Perrig Quemeneur, Bjorn Thurau, Kevin Reza, Jerome Cousin, Angelo Tulik.
Australia's Cadel Evans, the 2011 Tour de France overall winner, is competing in his home tour for the BMC Racing Team.