The 27-year-old from Maastricht, who became the first Dutchman to win the Giro in May this year, has already decided. He will compete in either the Giro or the Tour, but not both in 2018.
"I know already but I'm not going to tell you. Sunweb has its team presentation on January 5 and we will announce our programmes then," Dumoulin said.
He stood well-dressed for the cold outside the RAI television studios where organiser RCS Sport presented the 2018 Giro route on Wednesday evening.
Chris Froome announced on Wednesday that he would be riding the 2018 Giro d'Italia (Sunada)
(Image credit: Yuzuru Sunada)
"I go wherever I think I have the best chance of winning," he responded when asked if Froome's decision would affect his.
"I don't necessary feel that with Froome doing the Giro that my chance in the Tour is higher. It's not necessarily the right moment for me to go on to the Tour after winning the Giro.
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"I loved the Giro last year and I'm going to love if I do it again next year. I'm not going to say now that the Tour is the one for me next year."
The feeling is that the Tour is the one for Dumoulin in 2018. One close source told Cycling Weekly that he will not return to the Giro even if it was reported two days ago in the Italian sports daily La Gazzetta dello Sport that he would race.
Dumoulin's progression naturally points towards competing for the Tour overall. He surprised everyone, including himself, when he won mountain stages and took the early lead in the Vuelta a España in 2015. Only Fabio Aru (Astana) could eventually rip the lead from his hands on the final mountain day.
In 2016, he gave himself time to develop in the Grand Tours. He focused on stages, winning the Chianti time trial in the Giro, and a time trial and summit finish in the Tour. In 2017, he aimed for the overall classification in a three-week race and won the Giro.
"It's hard to say which suits me the best. They're both very challenging and very nice. I like both courses. They both have a little bit of everything but they're not perfect. The Giro is not perfect for me because it's lacking time trial kilometres, it's the same for the Tour," Dumoulin said.
"A perfect course would perhaps mean a less exciting race for the fans and that's not what the organisation wants. They made a nice course so that we can have a very challenging race."
The Giro includes two time trial stage, a 9.7-kilometre time trial in Jerusalem and a 34.5-kilometre time trial in the third week. The Tour organiser plans a 35-kilometre team time trial on day three and a 31-kilometre individual time trial on the penultimate day.
Froome will attempt to make history, to be the third rider to win three consecutive Grand Tours and to try for the Giro/Tour double.
"Will he be worn down in the Tour? I think he showed an even better in the Vuelta this summer than in the Tour, so you never know with him. But I don't look to other riders for making a decision about any kind of race," Dumoulin continued.
"It's challenging but he had some big challenges in the past and he showed that he's the best GC cyclist at the moment. If anyone can do it, I think it's him. Good luck to him."
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Gregor Brown is an experienced cycling journalist, based in Florence, Italy. He has covered races all over the world for over a decade - following the Giro, Tour de France, and every major race since 2006. His love of cycling began with freestyle and BMX, before the 1998 Tour de France led him to a deep appreciation of the road racing season.
