Butler is presumed to be the defensive coordinator in waiting in Pittsburgh, behind Dick LeBeau. He is very close with Cardinals coach Ken Whisenhunt (also a former Steelers assistant coach), however, and Butler likely will accept Arizona's defensive coordinator job if he's offered it, according to the source.
The Steelers expect LeBeau to return as defensive coordinator in 2011 -- and he has expressed a desire to do so -- but he always could opt to retire following the Super Bowl as well. If LeBeau continues to coach, he has said he would only do so in Pittsburgh, where the defense have been dominant under him. The Steelers led the NFL in scoring defense this season.