The Dutchman was scheduled to lead Giant-Alpecin in the first Monument of the year, but has come down with flu in the week leading up to the race.
Dumoulin revealed that the illness started at Paris-Nice last week, where he finished 12th in the general classification. He will be replaced by Bert De Backer in the eight-man lineup.
"It's disappointing for me to miss one of the biggest classics of the season," said Dumoulin. "It started at Paris-Nice. From Saturday to Sunday I had a sore throat and didn't feel completely well during Sunday's closing stage and once home it continued to get worse.
"It is a pity that I can't start Milan-San Remo but I need to accept it. I hope I will be fit in time for Catalunya and in the coming days we will know more."
It's another blow to Giant-Alpecin for the race they won last year with John Degenkolb, who misses the race due to injuries suffered in a collision with a car.
Coach Marc Reef said: "It's very unfortunate that Tom won't be starting on Saturday since he is considered as one of our riders capable of handling the tough finale at Milan-San Remo. Our plan will change slightly, which means that we will race more opportunistically and the aim is still to bring Simon [Geschke] to the finale as fresh as possible."
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Stuart Clarke is a News Associates trained journalist who has worked for the likes of the British Olympic Associate, British Rowing and the England and Wales Cricket Board, and of course Cycling Weekly. His work at Cycling Weekly has focused upon professional racing, following the World Tour races and its characters.
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