The UCI is investigating how a member of the public was able to drive onto the Il Lombardia course and hit Max Scachmann, leaving the German with a fractured collarbone.
"It is inadmissible to witness certain accidents in a WorldTour race," the CPA said afterwards. "We also want to know how the facts took place. Racing must be safer for athletes. We will never stop repeating it."
In the closing kilometres of the Italian Monument, as Schachmann was heading to a top 10 finish, a car drove onto the course around a bend, trying to head down a side road at the same time Schachmann was passing through. The Bora-Hansgrohe rider crashed into the back of the vehicle as the shocked driver got out and started apologising.
Furious, Schachmann continued to the finish, crossing the line in seventh place while gingerly holding his arm, having suffered a fractured collarbone.
"The UCI is investigating the circumstances of the crash caused by a private car in the final kilometres of the UCI WorldTour race Il Lombardia (Italy) on Saturday," cycling's governing body said in a statement.
"Events on the UCI WorldTour calendar are of the highest level and require fully closed roads at all times. The UCI will consider lodging a complaint with the Disciplinary Commission against the event organiser RCS Sport."
It was a day where crashes dominated racing, as Remco Evenepoel fell over a bridge and into a ravine, suffering a fractured pelvis and contusions to his right lung, but is considered lucky to have not come away with worse.
Meanwhile, Dauphiné race leader Primož Roglič also fell later in the stage and nearly abandoned, the Slovenian now questionable to start the final stage five.
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