"I'm well aware of what is at stake," he said. "But, when Rangers come knocking at your door, you don't turn things like that down.
"It's a fantastic chance for me and my family to come back up and it was too good an opportunity to turn down."
McGregor has established himself as first-choice goalkeeper since Smith's return to Rangers 12 months ago, but Alexander is prepared to battle for the gloves.
"As far as Scotland goes, I know the manager will want goalkeepers who are playing first-team football, so hopefully I can do well enough and we will see where it goes from there," said former Cardiff City goalkeeper Alexander.
"Allan is a fantastic goalkeeper and I am well aware of his capabilities. I have confidence in my own ability and know what I can do."