When McDonald says he has "unfinished business" down south I'm guessing that he means the business of earning more money, because it's not as if he's going to be joining a side looking to win trophies. He's simply assessing his options before making his decision, which he's perfectly entitled to do.
Saying that, I hope the club have said to him that the offer made has a finite lifespan, because if he's not interested we need to move on and look at other targets.