Former U.S. House speaker Dennis Hastert departs the federal courthouse in Chicago last year. (Christian K. Lee/AP)

The man whom former U.S. House speaker J. Dennis Hastert paid $1.7 million to keep quiet about a decades-old incident in which Hastert allegedly molested him is now suing the Illinois Republican for an additional $1.8 million he claims he is owed.

In the lawsuit, filed anonymously in circuit court in Kendall County, Ill., on Monday, the man alleges that he suffered severe panic attacks and bouts of depression and had to undergo long-term psychiatric treatment after the sexual abuse, which occurred when he was 14. He alleges that when he met with Hastert decades later to confront him about what he had done, Hastert agreed to pay him $3.5 million to compensate for the “pain, suffering, and harm” he had caused.

The man’s abuse allegations — and Hastert’s agreement to pay him — ultimately led to the criminal investigation of Hastert. According to federal authorities, the former House speaker, who became a lobbyist after leaving politics, began withdrawing money to pay the man in amounts that drew the notice of bank officials. When Hastert was asked about the withdrawals, he started taking money out in smaller increments so as not to trigger federal reporting requirements.

That itself is a crime, and it piqued the interest of the FBI. The bureau’s investigators would come to find that Hastert, who worked as a high school teacher and wrestling coach in Illinois early in his career, had abused or inappropriately touched as many as five teenagers in his care decades ago.

Hastert, 74, pleaded guilty last year to withdrawing money in increments meant to avoid federal reporting requirements, after federal prosecutors concluded that the statute of limitations had long passed on any of the alleged sex crimes. He is scheduled to be sentenced in federal court in Chicago on Wednesday.

Hastert admitted in his plea that he agreed to pay someone identified only as Individual A $3.5 million to “compensate for and keep confidential” prior misconduct against that person, and he admitted that he actually paid the person $1.7 million. The suit seeks the additional $1.8 million, plus interest — casting the verbal arrangement between the two men as a “settlement agreement” that Hastert breached.

The suit says the man never filed a lawsuit for the injuries he suffered because of the agreement and that he did not reveal his allegations to anyone “until he was required to truthfully answer questions from law enforcement personnel pursuant to the federal criminal investigation.”

Thomas Green, Hastert’s attorney, said he had not had time to review the lawsuit yet. Green had hinted in a previous filing that the victim was threatening to file such an action.

Kristi Browne, the man’s attorney, said Hastert had stopped paying her client “some time ago” and that his attorneys had not responded to their demand letters. “My client absolutely performed everything he promised to perform,” Browne said. “He absolutely has fulfilled his part of the bargain.”

Prosecutors have alleged in court filings that after Hastert was initially questioned about his unusual cash withdrawals, he claimed to FBI agents that he was being extorted and that the man now suing him was making false claims of sexual abuse. After listening to the man on a recorded call, though, agents found his claims to be believable, prosecutors have alleged.

In the lawsuit, the man alleges that Hastert abused him in a motel room after offering to take him to a wrestling camp designed for high school students, though the man, then 14, was not yet in high school. The man alleges that in 2008, he was “made aware for the first time that Hastert had abused someone else, too,” and he soon confronted Hastert about the years-old contact.

Browne declined to provide any identifying details about her client. She said he does not plan to attend Hastert’s sentencing.