Former Hoops star Miller was awestruck by the winger's Champions League performance against Benfica, capped by a winning goal.
"The way he played against Benfica tells me he has grown from a boy into a man. It was world class and that's the standard he has set himself.
"It will be difficult to reach that level every week but he's capable of it and has to keep improving.
"People all over Europe will have watched the game and McGeady will be the name on their lips.
"He has an end product and the goals will come. For now though he is right just to focus on being a winger.
"He won't be in any rush to leave but that won't stop top clubs looking at him. Celtic wouldn't sell a talent like Aiden for a penny less than £10m - maybe even £14m."