The 29-year old forward has been getting back to his best with the Fir Park club but could make his way to Parkhead at the end of the season as Hoops boss Neil Lennon shows considerable interest.
"It could be a possibility, there isn't any doubt about that," said McCall of the proposed summer shift.
"But if James has realistic ambitions of playing for Scotland, he has to be at a club where he's playing every week.
"We know what he's capable of, he just needs to be playing on a regular basis.
"He needs regular football and whether he'd get that if he went to Celtic I don't know.
"He's a Celtic supporter, but he's enjoying his time here and we'll just enjoy having him while we do."