The 43-year-old has been without a club since leaving the Scottish champions in May after four years in charge.
"They are two excellent clubs. Would I be interested in managing either of them? Of course I would," the Northern Irishman revealed on BBC Radio 5 live.
"I want a new challenge. I had a great challenge for four years at Celtic but I felt I had come to the end of the cycle there and wanted to do something else with my career."