The 20-year-old was set to make his debut in the Italian Monument after a breakthrough 2025, in which he won 14 times in his first season as a pro.
Brennan will be replaced by Victor Campenaerts in Visma-Lease a Bike's seven-man team for Milan-San Remo.
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A statement from Visma-Lease a Bike, shared on social media, read: "Unfortunately, Matthew has fallen ill and is not fit enough to start in Milano-Sanremo tomorrow. Victor will replace him."
The Dutch team's full line-up for the race is: Wout van Aert, Christophe Laporte, Victor Campenaerts, Edoardo Affini, Owain Doull, Timo Kielich and Matteo Jorgenson.
The team is expected to ride for Van Aert, who won the Monument in 2020.
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🇮🇹 #MilanoSanremo Unfortunately, Matthew has fallen ill and is not fit enough to start in Milano-Sanremo tomorrow. Victor will replace him. pic.twitter.com/c89eSalUhcMarch 20, 2026
Tom joined Cycling Weekly as a news and features writer in the summer of 2022, having previously contributed as a freelancer and been host of the TT Podcast. He is fluent in French and Spanish, and holds a master's degree in International Journalism.
An enthusiastic cyclist himself, Tom likes it most when the road goes uphill, and actively seeks out double-figure gradients on his rides. His best result is 28th in a hill-climb competition, albeit out of 40 entrants.
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