Sagan is racing in the Vuelta a España to prepare for the Worlds course that has 4,670 metres of climbing with a hard Igls climb.
"It's hard," Sagan replied to Cycling Weekly when asked about winning a fourth title.
"It's not obvious that I win it three times in a row and I'm going to win it a fourth time. Like everything should stop somewhere."
Sagan won in Richmond, Doha and Bergen, three years in a row. The Austrian course could be one too many for him, though he will go regardless with the Slovakian team to try.
"It's still far away and I don't think [I] could be really competitive with real climbers in that parcours."
Despite still suffering in training after his Tour de France crash, Sagan still came ready to the Vuelta. The three-time world champion has placed second three times so far.
"It's all of that, the first idea is to win stages, get good results, and also to prepare for the Worlds," Bora-Hansgrohe sports director André Schulze said. "But the worlds are difficult this year."
The team is getting behind all of its riders for the race with its headquarters only 80 kilometres away in Germany. Schulze explained the sponsors want that even if it is a national team event. "Also Peter wants to do his best," he added.
"The Vuelta is one of the best preparations for the Worlds given the parcours is so much climbing, I saw it in the Tour of the Alps, three laps, the climb is really hard. The best preparation is here in the Vuelta."
Sagan crashed in the 17th stage of the Tour de France and nearly abandoned. He fought ahead and won his sixth green jersey in Paris. He raced twice afterwards in one-day races, then travelled to Málaga for the Vuelta's start and with the Worlds in mind.
"[The Vuelta is] an easy race, well not an easy race, but a relaxed race," Sagan continued.
"I can stay here in good weather and train with the team. I stay with the team. I can still take some points. I'm not winning, but I can try!"
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