Rep. Jesse Jackson Jr. (D-Ill.), who took a leave of absence from Congress, is suffering from a medical condition more serious than "initially believed," according to a statement from his office.

The nine-term lawmaker is receiving "in-patient" treatment for "certain physical and emotional ailments," the statement noted. It did not provide additional details about his illness or how long he would be absent from Capital Hill.

"Congressman Jackson's medical condition is more serious than we thought and initially believed," Jackson spokesman Frank Watkins said. "Recently, we have been made aware that he has grappled with certain physical and emotional ailments privately for a long period of time."

The Illinois congressman had been on medical leave since June 10 because of exhaustion. He is receiving treatment at a medical facility, according to Watkins.

"At present, he is undergoing further evaluation and treatment at an in-patient medical facility," the statement continues. "According to the preliminary diagnosis from his doctors, Congressman Jackson will need to receive extended in-patient treatment as well as continuing medical treatment thereafter. We ask that you keep Congressman Jackson and his family in your thoughts and prayers during this difficult period."

Jackson is favored for reelection after fending off a tough primary challenge from former Rep. Debbie Halvorson (D-Ill.) earlier this year.

He could be in line to become a powerful subcomittee chairman on the House Appropriations Committee if Democrats win control of the lower chamber. If Rep. Nita Lowey (D-N.Y.) becomes chairwoman, he is in line to take over the State Department, Foreign Operations and related programs subcommittee.

Since his medical leave, Jackson's office had remained fairly quiet about his location and health. 

— Erik Wasson contributed

— This story was updated at 3:25 p.m.