Vic Fangio was the 49ers' defensive coordinator the past four seasons, but he agreed to the same position with the Bears on Tuesday morning.
How will San Francisco fill the void?
The 49ers are contemplating hiring Eric Mangini as Fangio's replacement, according to a report from the Sacramento Bee.
Mangini joined the 49ers in June 2013 as an offensive consultant.
He coached the team's tight ends in 2014.
On Monday morning, a report surfaced that Mangini would interview for the Raiders' defensive coordinator position.
Mangini was the Patriots' defensive backs coach from 2000 to 2004 before becoming New England's defensive coordinator in 2005.
He was the Jets' head coach from 2006 to 2008 and the Browns head coach in 2009 and 2010.
In 2011 and 2012, he was an analyst for ESPN.