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.”