At the hospital, the cyclist was diagnosed with a fractured collarbone and several ribs, Team Visma reports on the X social network.
The incident occurred on March 27, 67 km before the finish in the leading group. Three more cyclists received injuries of varying severity.
Van Aert, 29, is a silver medalist in the group race at the Tokyo Olympics and a three-time world champion in cyclocross.
Earlier, the Russian cyclist of the BORA - hansgrohe team, Alexander Vlasov, took third place in the second stage of the Vuelta Catalunya stage race.