Jerome Corsi, a conspiracy theorist and political commentator with connections to the former Trump adviser Roger J. Stone Jr., has been subpoenaed to testify on Friday before the grand jury in the special counsel investigation into Russia’s election interference and whether Trump associates conspired with the effort, his lawyer said on Wednesday.

The lawyer, David Gray, said that he anticipates that investigators for the special counsel, Robert S. Mueller III, plan to ask Mr. Corsi about his discussions with Mr. Stone, who appeared to publicly predict in 2016 that WikiLeaks planned to publish material damaging to Hillary Clinton’s presidential campaign.

“He fully intends to comply with the subpoena,” Mr. Gray said, adding that the subpoena was not specific about the topic but that he and his client anticipated “it has to do with his communications with Roger Stone.”

Mr. Mueller’s team appears to be zeroing in on Mr. Stone as a possible nexus between the Trump campaign and WikiLeaks, which was used by Russian intelligence officers to spread information stolen from Democrats, according to an indictment by Mr. Mueller’s team. Another former associate of Mr. Stone, the New York political gadfly Randy Credico, is also expected to testify before the grand jury on Friday.