Dumoulin has not raced since the Criterium, meaning he missed the Tour de France, but he is slowly getting back to full fitness.
Wiggins podcast: Sunweb let Dumoulin down, Jumbo-Visma won’t do the same to Roglic
"Two weeks ago, the tendon in my knee would become inflamed if I did too much, so I still have to be very careful, and it's meant that I haven't been able to train for more than two or three hours a day,” he said, per Cycling News.
"But I'd prefer to try to increase the intensity of the training, rather than the duration. I can climb quite fast again, but putting pressure on the knee when turning a corner is still painful.
"The hope is that from November I'll be able to use it to its full capacity again."
'It was okay until I stood up on the pedals' - Dumoulin talks about withdrawal
Dumoulin made headlines back in August when announcing he will leave Team Sunweb after eight years to join Jumbo-Visma.
With Vuelta a Espana champion Primoz Roglic and Wout van Aert for company at Jumbo-Visma, Dumoulin admits he is “hungry” to get back to racing.
'Lovely moment' - Roglic and Jumbo-Visma celebrate Vuelta win
"In the coming years, I actually think that having had this injury could turn out well," Dumoulin told Ten Dam, "because I'm fresh in my head again.
"I know where I want to go again," he said. "I'm hungry again."