A spokesperson for Paul Manafort is expected to testify before a federal grand jury in Washington on Friday.
Jason Maloni has been a longtime associate of Manafort, working with Trump's campaign chairman since 2007. He is known to have a vast knowledge of Manafort's business dealings and left a PR firm to continue working for him.
Asking a PR person is seen as peculiar move since such individuals are often privy to confidential information about their clients, often with access to personal matters and private documents.
While Maloni is not under investigation himself, it is unclear why prosecutors are seeking his testimony.
Manafort has been at the center of intense scrutiny from special counsel Robert Mueller in his probe looking for possible collusion between the Trump campaign and Russia. In July, the FBI raided his home seeking tax documents and other business records.
His business records and work on behalf of foreign governments, along with suspicions of money laundering, has been the target of Mueller's investigation, which has accelerated in recent weeks.
Despite the increased focus on Manafort by the grand jury and Mueller's team, he has not been charged with any wrong doing.
Maloni declined to comment for this story.