The defending champion came down in a low-speed crash in the peloton ahead of the first ascent of the Kwaremont, and remained prone on the road for several minutes while he received medical attention. He was later taken to hospital in nearby Oudenaarde.
Terpstra won the Ronde in 2018 in the colours of QuickStep before moving to Direct Energie ahead of the 2019 season.
His Direct Energie team was soon able to announce that it had "reassuring news" about Terpstra's condition. "Reassuring news about @NikiTerpstra who was able to come around after his fall," the team wrote on Twitter. "As soon as we have more news, we will communicate it."
A couple of hours later, the team added – again through Twitter – that the team's doctor could confirm that Terpstra was OK, but that he'd suffered a head trauma and had lost consciousness at the side of the road. "He will not be able to take part in Paris-Roubaix," it said.
Later in the evening, Terpstra's management agency, SEG Cycling, tweeted that Terpstra had indeed suffered severe concussion and wouldn't be racing at Roubaix next weekend as a result of his spring Classics campaign now being over.
"Recovery is needed now," the message added. "On behalf of Niki, we thank you for all the support and hope everyone can let him rest and heal from this."