Updated: 11:23 p.m.

White House Chief of Staff Rahm Emanuel will announce as soon as Friday whether he is going to run for Chicago mayor, a source close to Emanuel said Monday night.

“Rahm is nearing a decision on whether to leave the White House and explore a run for mayor of Chicago,” the source said. “An announcement could come as early as Friday. Because of family considerations, no final decision has been made.”

CNN reported that Emanuel is all but certain to run for the slot being vacated by Chicago Mayor Richard Daley, who surprised many when he announced earlier this month that he will not seek re-election after holding the seat for 21 years. Emanuel’s campaign team is already being formed, and an announcement is expected Friday, CNN reported.

Several news reports have speculated that Obama adviser Pete Rouse will serve as interim chief of staff if Emanuel leaves. Rouse was chief of staff to Obama when he served in the Senate. He also was chief of staff to former Senate Majority Leader Tom Daschle (D-S.D.) for 19 years.