With 40 kilometers to go in Flèche Wallonne, the Dane crashed onto the slippery asphalt, looking visibly bruised as he got back on his feet.
Skjelmose got back on his bike after a few minutes, but Lidl-Trek announced shortly afterwards that he had withdrawn from the race.
It is still uncertain whether Skjelmose sustained any injuries.
Tadej Pogacar won the race after racing clear of the peloton at the Mur de Huy towards the end.
The reigning World Champion won by nine seconds ahead of Kévin Vauquelin (Arkéa–B&B Hotels) and Tom Pidcock (Q36.5) who took second and third respectively.
Pogacar's strength in the end was underlined by the fact that it was the biggest winning margin in the men’s race since 2003