(CNN) - Rep. Jesse Jackson Jr. returned Tuesday for a "follow-up" at the Mayo Clinic, where he had been in treatment for what he called "several serious health issues."
The Illinois congressman left the clinic in early September, and a statement distributed by clinic spokesman Nick Hanson on Jackson's behalf said he returned "for follow-up evaluation to ensure he is on the path to properly manage his health."
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Jackson, 47, has been away from Congress and largely out of the public eye since May, and his office said in June that he was taking a leave of absence. In August, it emerged that the nine-term Democrat was suffering from depression and was in treatment at the Mayo Clinic.
After meeting with Jackson in August, Rep. Patrick Kennedy told CNN that his longtime friend and colleague was suffering from "serious depression - deep, deep depression."
In a recorded phone call made to constituents on Saturday, Jackson said he has "undergone medical treatment to address several serious health issues."
"Like many human beings, a series of events came together in my life at the same time and they've been difficult to sort through," he said in the call, which his office provided to CNN. "I am human, I am doing my best, and I am trying to sort through them all."
He is the subject of an investigation involving possible financial improprieties conducted in Washington by the FBI and federal prosecutors, a federal law enforcement official told CNN last week. The Wall Street Journal reported the investigation involved home improvements which may have been improperly funded by campaign donations.
Jackson is also under investigation by the House Ethics Committee, which is examining allegations that, in 2008, he or one of his associates offered to raise money for then-Illinois Gov. Rod Blagojevich in exchange for Jackson being appointed to the Senate seat vacated by Barack Obama.
"I am anxious to return to work on your behalf but at this time, it's against medical advice," he said in the call. Asking for patience, he added, "The good news is my health is improving, but my doctors tell me the road to recovery is a long one."
Jackson is the son of the famed civil rights leader of the same name and represents Illinois' 2nd Congressional District.
– CNN's Miriam Falco contributed to this report