The Dutchman, who will look to defend his rainbow stripes on Wednesday, won the title last year in Norway ahead of Primož Roglič (LottoNL-Jumbo) and Chris Froome (Sky).
Australian Dennis, the former hour record holder, comes to Austria after winning both individual time trials in the Vuelta a España.
"Obviously Rohan Dennis," Dumoulin told Het Nieuwsblad when asked about his top rival.
"On paper, it becomes a battle between me and him, but everything is possible at a World Championship.
"I still remember the World Championships in Richmond. They said Dumoulin, Martin and Dennis would be on the podium, only the order had to be determined. In the end, none of us had a medal."
The Tour de France time trial to Espelette was his favourite day wearing the stripes, "It was really number one," Dumoulin said.
Dennis has signed for team Bahrain-Merida for the 2019 season. This 2018 season, he wore the pink jersey at the Giro d'Italia thanks to finishing second to Dumoulin in the opening time trial and taking time bonuses in the second stage. He then won the 34.2km time trial stage ahead of Tony Martin (Katusha-Alpecin) and Dumoulin.
Dennis is still in search of his first rainbow jersey, and said "me and Tom" when asked to name the top favourites.
Thinking about Wednesday and the 52.5 kilometres, Dumoulin laughed when asked to choose 'favourites' for the race. He said, "We all know that the paper may be in the trash can on Wednesday afternoon."
Dumoulin spent time training in Livigno, Italy, at altitude. He joined the defending women's time trial champion, Dutch rider Annemiek Van Vleuten on rides. "She didn't just sit on my wheel," he added. "Annemiek can ride hard, especially uphill. She could easily participate in the six-hour training sessions."
The women race later Tuesday afternoon, Dumoulin, Dennis and the rest of the men start 24 hours later.
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