Butler is the coach-in-waiting behind Dick LeBeau as Pittsburgh's defensive coordinator, but he is intrigued by the Cardinals' opening, and Steelers officials expect him to take it. A Steelers source said the team likely wouldn't block the move.
Monday is the first day the Cardinals can officially approach Butler for permission to interview, and they intend to do just that. Butler is close with Cardinals coach Ken Whisenhunt from their time together on the Steelers' staff, and their friendship extends beyond football.
The Steelers are hopeful that LeBeau will return for another season -- and he has indicated he plans to -- though retirement is a year-to-year proposition.
LeBeau's contract is set to expire, and the Steelers would very much like to keep him.