Lawyers for Michael Flynn notified the president's legal team in recent days that they could no longer discuss the investigation by special prosecutor Robert Mueller, the Times reported, citing four people involved in the case.
The development indicates that Flynn is cooperating with prosecutors or is negotiating such a deal, the report said.
Flynn's lawyers had been sharing information with Trump's legal team about Mueller's probe related to Russian interference in last year's ballot, which saw Trump defeat his Democratic challenger Hillary Clinton.
"That agreement has been terminated," the Times' sources said.
He was forced to resign three weeks later over his Russia contacts.
Mueller's investigation has already led to the arrest of Trump's one-time campaign chairman Paul Manafort, Manafort's partner Rick Gates, and George Papadopoulos, a campaign foreign policy advisor. Papadopoulos pleaded guilty to lying to the FBI.
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