Turkish basketball star Enes Kanter was refused entry into Romania on May 20 after he was told his passport had been canceled by the Turkish Embassy.
Kanter, who plays in the NBA, is a supporter of U.S.-based Muslim leader Fethullah Gulen, whose extradition is being sought by Turkey for his alleged role in the July 2016 coup attempt against Turkish President Recep Tayyip Erdogan.
Gulen, who has lived in self-imposed exile since 1999, has denied any involvement in the attempted government takeover.
Kanter -- who was eventually allowed to fly to London and was due to return to the United States -- said his passport was canceled because of his political views.
Kanter said in a video posted to his Twitter page that Erdogan is "a dictator," citing last week's attack on protesters outside the Turkish ambassador's residence as proof.
"He's attacking people in Washington -- he's a bad, bad man," Kanter said.
Kanter said last year he had severed ties with his family after Turkish media published a letter signed by Kanter's father in which he said he was "disowning" his son.
Turkish officials have arrested or fired tens of thousands of people for their alleged support of Gulen since the coup attempt.