Former Rep. Jesse Jackson Jr. has signed a plea deal regarding the inappropriate use of official funds, Fox News has learned.

Details of the deal are unclear, but Fox News has learned that it also pertains to a "social acquaintance" of the former Illinois Democratic congressman.

The Chicago Sun-Times reports that the deal -- at least one being considered earlier in the week -- includes "significant jail time."

Jackson resigned last November shortly after being reelected to the House. The son of civil rights leader Jesse Jackson Sr. had been treated for bipolar disorder, but also has been the subject of an ongoing federal investigation over campaign funds.

The Sun-Times reported that the probe has split into two separate investigations, with one into Jackson's wife Sandi. Sandi recently resigned as a Chicago city alderman.

The confirmation of a plea deal marks another blow for a public figure who was once considered a rising star.

Jesse Jackson Jr. first took office in 1995 after winning a special election and began his career in Washington with a star power and pedigree that set him apart from his hundreds of other House colleagues.

But despite high expectations, he largely went unnoticed as a policymaker. Instead, he gained a reputation for quixotic pursuits such as trying to impeach President George W. Bush and push through constitutional amendments that had no chance.

Jackson, 47, disappeared in June, and it was later revealed that he was being treated at the Mayo Clinic for bipolar disorder and gastrointestinal issues. He returned to his Washington home in September but went back to the clinic the next month, with his father, the Rev. Jesse Jackson, saying his son had not yet "regained his balance."

Fox News' Mike Levine and Chad Pergram and The Associated Press contributed to this report.