The source also said the Huskers are trending toward hiring Phil Snow as associate head coach and Terry Bradden as defensive line coach to replace Terrance Knighton, who followed White to Tallahassee.
Butler, 51, joined head coach Matt Rhule's staff from the Buffalo Bills in July. Butler came to Lincoln with 20 years of experience in college football, including on Bill O'Brien's staff at Penn State, where he spent 2012 coaching the secondary before taking over as defensive coordinator in 2013.
Snow worked with Rhule at multiple stops as his DC. Bradden would come to the Huskers after eight seasons with the NFL's Kansas City Chiefs, the past four as assistant defensive line coach.