The Jumbo-Visma rider was hoping to be the strongest rider in his team at the Spanish Grand Tour, but has since said he’s not feeling at his best.
Stage one of the Vuelta was an explosive day of racing as the general classification contenders took up the fight early, with Dumoulin’s team-mate Primož Roglič emerging as the leader.
Dumoulin slipped back on the tough climbs to Arrate, finishing the stage 51 seconds down on Roglič, making his challenge that little bit tougher.
Speaking after the stage, the Dutchman told broadcaster NOS: “That's how we went into the race, see who was the strongest. That became very clear today.
“I’ll do my best here and then we'll see, I started with that mindset. In any case, today was not good enough."
Dumoulin added: "I just don't feel one hundred percent, just a little tired. I hope I can get through this round."
The 29-year-old has suffered a rough few seasons, struggling with injury in 2019 and then illness in early 2020.
He returned to Grand Tour racing at the Tour de France, where he was never in contention for the win, but still finished seventh overall.
Dumoulin had hoped his form would improve for the Vuelta, as Jumbo-Visma try to make up for the disappointment of losing the Tour with Roglič one day from Paris.
But Roglič has once again emerged as the strongest rider in the team, winning stage won and taking the leader’s jersey with a five-second advantage to his nearest rival, Richard Carapaz (Ineos Grenadiers).
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