In an interview with the Vulture website, the man, who spoke on condition of anonymity, said he took part in an acting class taught by Spacey when he was 12.
Two years later, they began what the man described in the interview as a "sexual relationship."
Then when he was 15, Spacey attempted to rape him at his apartment, the man said, after which he ended the relationship.
"I would call him a pedophile and a sexual predator," he said.
Eight people who worked on the "House of Cards" political drama meanwhile told CNN that the actor engaged in sexual harassment on set, typically targeting young men, while one of the eight said Spacey sexually assaulted him.
Netflix has indefinitely suspended production of "House of Cards" in the wake of allegations against Spacey, after already announcing that the upcoming sixth season of the show would be its last.
Actor Anthony Rapp opened the floodgate of harassment and assault allegations against the double Oscar winner when he said that Spacey made a "sexual advance" when he was a 14-year-old boy more than 30 years ago.
