Former U.S. Attorney Preet Bharara said Sunday that President Donald Trump should be “very worried” about his former national security adviser Michael Flynn cooperating with prosecutors if Trump has “done bad things.”

“It depends on what the president has done and what the president’s conversations with Michael Flynn and others have been,” the former U.S. attorney for the Southern District of New York said on CNN’s “State of the Union.” “But if you have done bad things, then you should be very worried.”

Flynn’s lawyers have notified Trump’s legal team that they can no longer share information about the investigation by special counsel Robert Mueller, which could mean that Flynn is cooperating or working on a deal to cooperate with the inquiry.

Bharara, who was fired by Trump, said there’s a good chance Flynn has flipped or is negotiating a deal.

“Based on how things used to operate in my office and based on the way the world works, is that there’s a substantial likelihood that they are at least in discussions with respect to cooperating,” he said.

“Now, that could fall apart because maybe he’s not disclosing everything, he’s trying to protect or he’s trying to minimize, and the prosecutors decide not to sign him up to a deal. But I think that the likelihood is that that is what they are talking about.”

Flynn, who was fired just a few weeks into Trump’s presidency, is viewed as vulnerable to potential criminal charges over his lobbying work and failure to disclose foreign contacts.