Renato Seabra, 20, had been staying with Carlos De Castro, 65, at the InterContinental Times Square, The New York Times reported. De Castro's body, beaten and castrated, was found in his hotel room Friday.
Seabra was arrested at Roosevelt Hospital, not far from the InterContinental, the New York Daily News reported. A nurse called police after she saw his injuries.
Police said Seabra was being held at Bellevue Hospital under guard and was likely to be charged with murder.
"Right now he's in our custody, he's not charged and he's undergoing a psychiatric evaluation," a police source told the Times.
The two men had a loud argument Thursday at Paulinos, a restaurant in the East Village, the New York Post reported. Sources told the newspaper Seabra told de Castro he had only been with him for money and that he preferred women.
De Castro was well known in Portugal as a writer on fashion and gay rights, the Times said.