Avenatti posted a Twitter message saying he intends to fight the "legally baseless allegations" and vowed to clear his name. He said he expects the indictment to be handed up within the next 48 hours.
The U.S. Attorney's Office in Manhattan declined to comment. Avenatti, 48, was arrested in March after federal prosecutors said he threatened to expose that Nike improperly paid high school basketball players unless the company paid him up to $25 million.
He has denied those allegations and separate charges of tax, wire and bank fraud in California. Prosecutors there say Avenatti embezzled settlement funds and proceeds from other matters he handled for several clients.
Avenatti described the New York indictment as "the formal charging document that usually follows a criminal complaint, which is what was issued in connection with my arrest." He said he intends to plead not guilty to the charges.
"I look forward to the trial where I can begin to clear my name," he wrote on Twitter. Avenatti rose to fame representing porn actress Stormy Daniels in her legal battles against President Donald Trump.
Prosecutors haven't said whether they believe Avenatti's information about Nike was accurate, but they say he crossed a line by trying to enrich himself with threats.