FILE PHOTO: Former U.S. President Donald Trump campaign aide Rick Gates departs after a status conference at the U.S. District Court following his indictment on tax fraud and money laundering charges in the special counsel's investigation into alleged Russian meddling in the 2016 U.S. presidential election in Washington, U.S., November 2, 2017. REUTERS/James Lawler Duggan/File Photo

WASHINGTON (Reuters) - Rick Gates, a star prosecution witness in the tax and bank fraud trial of former Trump campaign chairman Paul Manafort, is due to testify on Monday, a defense lawyer said.

Manafort lawyer Kevin Downing said Gates would be the next witness called in the federal trial in Alexandria, Virginia. Gates is cooperating with an investigation by U.S. Special Counsel Robert Mueller and will be called to testify against his former boss.