The German national champion was on the final descent when an unauthorised vehicle veered on to the course, cutting across the blindsided Schachmann who hit the car before crashing off his bike.
The Bora-Hansgrohe rider was quick to get back on the bike to finish seventh, but questions remain over how the car made its way onto the course.
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Schachmann's was the second incident of the day after Deceuninck–Quick-Step rider Remco Evenepoel crashed over a wall and fell into a ravine. The 20-year-old was conscious as he was transported to a local hospital.
It is also the second incident involving a car after Milan-Sanremo in 2018.
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