The Dutchman, who made his 2020 road debut at last week's Volta ao Algarve, was suffering from flu and a high fever on Wednesday night, the team announced as they posted their squad for the race to Instagram.
Van der Poel was due to compete at the race for the first time in his career in the Opening Weekend before heading to Italy for Strade Bianche and Milan-San Remo. He would then race the Volta a Catalunya before racing Dwars door Vlaanderen, the Tour of Flanders, Paris-Roubaix, Brabantse Pijl, Amstel Gold Race and La Flèche Wallonne.
Last year, Van der Poel rode his fullest spring campaign yet, taking wins at the GP Denain, Dwars door Vlaanderen and Brabantse Pijl before a stunning late comeback at Amstel Gold Race saw him triumph in the Netherlands' biggest race while wearing the national champion's jersey.
The 25-year-old enjoyed a quiet race in Algarve, telling Belga News Agency on the final day that he was planning to compete for victory at Omloop Het Nieuwsblad.
"Of course, I'm going to compete at the front, to win," he said. "A week can make a big difference to me. Algarve has really pleased me; it went better than expected."
Floris De Tier, a new signing from Jumbo-Visma, will take Van der Poel's spot on Alpecin-Fenix's Omloop Het Nieuwsblad team. He'll join Algarve mountain classification winner Dries De Bondt, as well as five other new signings – Senne Leysen, Kristian Sbaragli, Otto Vergaerde, Scott Thwaites, and Petr Vakoč.
Alpecin's Kuurne-Brussel-Kuurne squad has also undergone changes, with Sacha Modolo missing out due to flu and Oscar Riesebeek suffering an ankle injury. The pair are replaced by De Bondt and Roy Jans.
Here is our squad for @omloophetnieuwsbladofficial! 👌 @mathieuvanderpoel will not be at the start of Omloop Het Nieuwsblad this weekend. Van der Poel has the flu and because of high fever starting Wednesday night, he won’t be able to race... 🤒 #AlpecinFenix #OHN20 Alpecin-Fenix
A photo posted by @alpecinfenix on Feb 27, 2020 at 6:52am PST