Veteran Australian Mathew Hayman blamed the service cars for a crash which forced him to retire from what may be his final world championships road race.
The 2016 Paris-Roubaix champion said he had "nowhere to go" when service cars came to a sudden halt on a corner on the 19.1-km lap.
Hayman did not sustain any serious injuries in the crash.
The 39-year-old's disappointment was even greater because it was possibly his last world championships, where he was riding in support of Michael Matthews, one of the pre-race favourites on Sunday's 267.5-km course.
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"I'm not sure if I actually hit the car. I came pretty close. I was coming back from a stop and I have the feeling that a lot of the guys here in the convoy don't drive the rest of the year at races," Hayman told reporters.
"A whole bunch of cars just stopped and no one seemed to want to give the riders the right of way. Maybe I expected too much from the convoy. Normally the guys I'd race with, the drivers you're with, in these races, they know when a rider is coming back and they give way.
"All the cars were stopped in the second corner before the descent, before going into the tunnel. They seemed to all misjudge it. They stopped quickly and that pushed me onto the wrong side of the road."