CHICAGO -- U.S. Rep. Jesse Jackson Jr., who has given no hint of when he'll return to work four months after taking medical leave, will head back to the Mayo Clinic for a checkup "soon," his father, the Rev. Jesse Jackson, said Sunday.

The Democratic congressman from Illinois was released from the Rochester, Minn., clinic in September after seeking treatment for bipolar disorder and gastrointestinal issues. He has been with his family in Washington since, but has not appeared in public, campaigned beyond a recent robocall or said when he'll return to Capitol Hill. His spokesmen will only say that Jackson remains on the Nov. 6 ballot.

Jackson's father, a prominent civil rights leader, said the congressman will go back to Mayo in the near future, but would not say when or for how long. He said only doctors could determine if he would be able to return home immediately or receive further inpatient treatment.

"He has not regained his balance altogether," the elder Jackson said. "But he's seeking his balance."

He said his son has an "overwhelming desire to get back to work," but any predictions were premature.

Mayo Clinic spokeswoman Duska Anastasijevic said Jackson is not a current patient and she could not confirm whether he has plans to check into the clinic. Jackson spokesman Frank Watkins said he didn't have any further information.

Many questions about the congressman's medical leave have gone unanswered. He first took medical leave in June for what staff described as exhaustion, but the information wasn't disclosed publicly until two weeks later.

Since then, information has come in spurts. It took weeks for his office to say where and for what Jackson was being treated.

The timing of his leave also has invited scrutiny.

Jackson – just weeks from the election – remains under a House Ethics Committee investigation for links to imprisoned former Gov. Rod Blagojevich. The committee is looking into allegations that Jackson was involved in discussions about raising money for Blagojevich's campaign in exchange for an appointment to President Barack Obama's vacated U.S. Senate seat. And the announcement of the leave came just days after a former fundraiser connected to those allegations was arrested on unrelated federal medical fraud charges.

Jackson has repeatedly denied any wrongdoing and has said his name will be cleared.

More recently, the Chicago Sun-Times reported that there is a federal probe related to his campaign finances.

The congressman, who first won office in 1995 special election, faces two little-known candidates on the November ballot. He's widely expected to be re-elected to a ninth full term despite the fact that he has not appeared in public for months. Jackson's Chicago-area district is heavily Democratic and many community leaders and mayors have endorsed him.

Jackson has said recently that he sees doctors twice a day while at the family's home in Washington. His wife, Chicago Alderman Sandi Jackson, has said that only doctors will be able to say when he can return to work.

The congressman's first communication to the public since the leave came Saturday in a robocall to voters in which he asked for patience.

"I am anxious to return to work on your behalf, but at this time it is against medical advice, and while I will always give my all to my constituents, I ask for your continued patience as I work to get my health back," he said in the recorded call.

His opponents – a Republican college professor and postal worker running as an independent candidate – blasted the move.

"As we wait for the Congressman to return, we have no voice. And now the Congressman is saying he has no answer about when he will return," Republican Brian Woodworth said in a statement late Saturday.

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Associated Press writer Sara Burnett contributed to this story.

Earlier on HuffPost:

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  • Jesse Jackson Jr.

    FILE - In this March 21, 2010 file photo, Rep. Jesse Jackson, Jr., D-Ill., uses his PDA to photograph demonstrators outside on the U.S. Capitol as the House prepares to vote on health care reform in Washington. When Jackson disappeared on a mysterious medical leave in June 2012, it took weeks for anyone in Washington to notice. Jackson has never lived up to the high expectations on the national stage.

  • Jesse Jackson, Jr.

    FILE - In this Jan. 5, 2011 file photo, Rep. Jesse Jackson, Jr., D-Ill., is pictured before a ceremonial swearing in of the Congressional Black Caucus on Capitol Hill in Washington.

  • Jesse Jackson Jr.

    FILE - In this May 16, 2011 file photo, U.S. Rep. Jesse Jackson Jr. attends ceremonies for Chicago Mayor-elect Rahm Emanuel in Chicago. (AP Photo/Charles Rex Arbogast, File)

  • Jesse Jackson Jr.

    FILE - In this Tuesday, March 20, 2012 file photo, U.S. Rep. Jesse Jackson Jr., D-Ill., thanks supporters at his election night party in Chicago. Jackson's office announced Monday, June 25, 2012 in a news release that the congressman has been on a medical leave of absence since June 10 and is being treated for exhaustion. (AP Photo/M. Spencer Green, File)

  • Jesse Jackson Jr., Sandi Jackson

    U.S. Rep. Jesse Jackson Jr., D-Ill., and his wife Chicago Alderman Sandi Jackson, thank family members at his election night party Tuesday, March 20, 2012, in Chicago after his Democratic primary win over challenger, former Rep. Debbie Halvorson, in the Illinois' 2nd District. (AP Photo/M. Spencer Green)

  • Jesse Jackson Jr., Sandi Jackson

    U.S. Rep. Jesse Jackson Jr., D-Ill., and his wife Chicago Alderman Sandi Jackson, embrace at his election night party Tuesday, March 20, 2012, in Chicago after his Democratic primary win over challenger, former Rep. Debbie Halvorson, in the Illinois' 2nd District. (AP Photo/M. Spencer Green)

  • Timothy Geithner, Jesse Jackson Jr.

    Treasury Secretary Timothy Geithner, right, declines an offer by U.S. Rep Jesse Jackson Jr., D-Ill., to talk to reporters during a tour of the Ford Motor Company Stamping Plant in Chicago Heights, Ill., Wednesday, April 4, 2012. (AP Photo/Charles Rex Arbogast)

  • U.S. Rep. Jesse Jackson Jr., Sandi Jackson

    U.S. Rep. Jesse Jackson Jr. and his wife, Chicago Alderman Sandi Jackson, ask each other for their support and votes as they arrive at a polling station for early voting, Friday, March 9, 2012, in Chicago. (AP Photo/M. Spencer Green)