With just weeks before Reza Zarrab, a Turkish gold trader who has been charged in Manhattan with conspiring to violate the United States sanctions on Iran, is to go on trial, his lawyers have given every indication that he may be prepared to plead guilty.

If so, it would be a startling turn of events for Mr. Zarrab, who has been aggressively battling his widely watched legal case ever since his arrest in 2016, hiring a dream team of lawyers and seeking dismissal of the charges.

He even retained Rudolph W. Giuliani, the former New York mayor, in an effort to try to persuade the Trump administration and Turkey’s president, Recep Tayyip Erdogan, to agree to a diplomatic resolution to his case.

But in court papers filed on Monday, lawyers for Mr. Zarrab’s co-defendant, a Turkish banker named Mehmet Hakan Atilla, wrote that Mr. Zarrab “has essentially not participated in the case” since September, and it seemed “likely that Mr. Atilla will be the only defendant appearing at trial.”