(CNN) Robert Mueller may not be through with Rick Gates, a deputy Trump campaign aide and one of the four people who have been charged as part of the special counsel probe into Russian meddling in the 2016 election.

In a court appearance Monday in Manhattan, Gates' attorney Walter Mack said that federal prosecutors have told him that more charges, called superseding indictments, may be coming.

"We don't know what the government is going to do," Mack said in court, referring to both Gates' case and a white-collar case in New York involving one of Gates' business partners. "I mean, in both cases we've been told that there may be a superseder. We don't know what's happening."

Mueller charged President Donald Trump's former campaign chairman Paul Manafort and his deputy, Gates, on October 30 with 12 alleged crimes related to money laundering and foreign lobbying violations. Both have pleaded not guilty. The charges against Manafort and Gates are unrelated to the Trump campaign, though it's possible Mueller could add additional federal charges.

Mack represents both Gates in DC and his business partner in New York. Neither is a witness or co-defendant in the other's case, federal prosecutors say, but attorneys from Mueller's special counsel investigation have raised the possibility that a conflict of interest could arise between the two men and their attorney.

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