June 26, 2012 -- Staffers for Congressman Jesse Jackson Jr., son of an African-American icon and the subject of a House ethics investigation, said today they do not know when their boss will return to work after announcing that he has quietly been on a leave for the past two weeks because of "exhaustion."

The statement was released by Jackson's office late Monday night. His office has been open during that time, but the congressman had not been appearing on the Hill or on the House floor for votes.

"On Sunday, June 10th, Congressman Jesse L. Jackson, Jr. went on a medical leave of absence and is being treated for exhaustion. He asks that you respect his family's privacy. His offices remain open to serve residents of the Second District," read a statement from his office.

Asked if staffers had received any word on Jackson's condition or when he planned to return to work, a spokesman said, "No."

Jackson's Twitter account remained active on Monday, twice posting about the Affordable Care Act, but it was unclear if Jackson had personally sent the messages.

Jackson, a Democrat from Chicago first elected to Congress in 1995, is running for re-election this years. Calls to his campaign to determine the status of his race were not immediately returned.

The House Ethics Committee is investigating allegations that Jackson offered to donate money to then Illinois Gov. Rod Blagojevich's gubernatorial campaign in exchange for the Senate seat vacated by President Obama.

A witness in Blagojevich's 2010 corruption trial linked Nayak to Jackson's alleged attempt to buy Obama's seat from Blagojevich.

Blagojevich was found guilty of corruption and began serving a jail term earlier this year.

Jackson has denied the accusation.

Jackson is also being investigated for allegedly directing Raghuveer Nayak, a political donor and friend, to pay for air fare and travel accommodations for a woman Jackson calls a "social acquaintance."

Nayak last week was indicted by a grand jury on different fraud charges related to outpatient medical clinics.

Jackson's father is the Rev. Jesse Jackson, a civil rights leader and one-time presidential candidate.