Skjelmose on Saturday fell heavily in the rain after colliding with a traffic island at around 50 kilometres from the stage finish.
His head bounced off the asphalt, making the crash look even worse. He stayed down and remained conscious but it was clear he was in serious pain.
His Lidl-Trek teammates checked on his health immediately after the incident and later the Danish climber was wrapped in blankets and loaded into an ambulance with ripped shorts and an injured right thigh.
A short update from Lidl-Trek on social media read: "Skjelmose is on the way to hospital via ambulance, we will provide updates when we are able to."
Skjelmose, who was expected to be among the contenders for the win at Auron, with a 7.3km, 7% climb at the end of the stage, was third in the overall standings, 59 seconds off race leader Matteo Jorgenson (Visma-Lease A Bike), heading into today's stage from Nice to Auron.
Michael Storer (Tudor Pro Cycling Team) took a fine solo victory on the penultimate stage of Paris-Nice, which moved the Australian up to fourth place in the general classification.