On Sunday, a photo of Kim Woo-bin was uploaded to an Instagram account falsely claiming to belong to the actor.
The account does not belong to Kim, a representative of Sidus HQ, Kim's management agency, said Monday.
"Kim does not have any social media accounts," the representative said. The uploaded photo was one taken a long time ago, the representative added.
"We have expressed numerous times that the account does not belong to Kim, yet news reports keep popping up," the representative said. "We will deal with the account."
The account has sparked outrage among fans of the model-turned-actor.
Kim was diagnosed with nasopharyngeal cancer, a rare type of head and neck cancer, in May.
He has halted all filming activities and is concentrating on treatment.
The shooting schedule for the film "Wiretap," in which Kim was set to star, has been postponed.