Members of his prominent family — including his father, civil rights leader Rev. Jesse Jackson — also have been mum. The elder Jackson declined to speak about his son Wednesday.
The timing of the leave also has raised questions, since it comes as Jackson is under a House Ethics Committee investigation for ties 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 the then-governor appointing him 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.
Jackson, who first won office in 1995, is on the November ballot with two little-known candidates. He's widely expected to win re-election.