Mr. Avenatti could not be reached for comment.
A veteran plaintiffs lawyer, Mr. Avenatti rose to fame in March 2018 when he filed a lawsuit against Mr. Trump on behalf of Ms. Daniels, the pornographic film actress who said that she had an affair with Mr. Trump and had received a hush-money payment leading up to the 2016 election.
Mr. Avenatti became a fixture on cable news, leveraging Ms. Daniels’s case to build his own profile as a foil to Mr. Trump. He was even taken half-seriously when he declared that he was interested in making a presidential run in 2020.
Ms. Daniels’s suit, which sought to invalidate a nondisclosure agreement, was dismissed by a federal judge in California this month, and a separate defamation suit Mr. Avenatti filed against Mr. Trump was similarly dismissed late last year. The discussion about Ms. Daniels, however, has remained a leading sore point of the Trump administration, as checks made out to her with the president’s signature on them were given to Congress last month by his former personal lawyer, Michael D. Cohen, who has pleaded guilty to federal charges.
Last September, Mr. Avenatti also inserted himself into the confirmation hearings of Justice Brett Kavanaugh. The week before Justice Kavanaugh was confirmed, Mr. Avenatti announced that he had a new client, Julie Swetnick. Ms. Swetnick said that she had witnessed sexual misconduct by Justice Kavanaugh and some of his friends at high school parties in the Washington area in the early 1980s, when she was a college student in Maryland.
As Mr. Avenatti’s national profile grew, so did his legal and financial troubles.
He was arrested in Los Angeles in November on suspicion of domestic violence, which he called an effort to intimidate him, though he was not charged with any crime. His firm has repeatedly filed for bankruptcy, most recently on March 7, in Santa Ana, Calif.
The charging documents in the Nike case refer to an unnamed co-conspirator, another lawyer who worked with Mr. Avenatti. That lawyer is Mark Geragos, according to a person with knowledge of the investigation who requested anonymity because of an inability to speak publicly.
Mr. Geragos, a top celebrity lawyer, is best known in the sports world for representing the former quarterback Colin Kaepernick in his collusion case against the N.F.L., which was recently settled. He also played a role in Mr. Kaepernick’s negotiations with Nike over 2017 and 2018, which resulted in Nike’s making Mr. Kaepernick one of its highest paid football endorsers and a face of a new advertising campaign.