It was on Thursday when lawyers for a Turkish banker on trial in Manhattan federal court told the judge that their client would take the stand the next day, to testify on his own behalf.

The banker, Mehmet Hakan Atilla, 47, had been charged with conspiring to violate United States sanctions on Iran in a case that has drawn much attention in Turkey, including from that country’s president, Recep Tayyip Erdogan, who has repeatedly criticized the prosecution.

Mr. Atilla, who was on a business trip in March when he was arrested at Kennedy International Airport, has been a kind of forgotten man in the case, overshadowed by his co-defendant, Reza Zarrab, a wealthy Turkish-Iranian gold trader.

Mr. Zarrab, who is 34 and married to a Turkish pop star, had lived a celebrity life in Turkey. He was arrested in March 2016 on a family trip to Disney World and sent to Manhattan to face trial.