The full-back has been attracting Premier League attention in recent weeks.
The 18-year-old only became a first-team regular for the Hoops this season, but has already started to attract attention from south of the border, with the Record reporting that both Southampton and Manchester City are interested in bagging his signature.
But McStay - who rejected a move to Juventus during his career (via Record) so sees parallels between himself and the prospect - has suggested that staying exactly where he is would be the best decision for him currently.
"He should enjoy his development at Celtic. There are a lot of similar things because he is in the team early, he travelled to watch Celtic with his family and he's a supporter of the club," he told the Record.
"I never had a left foot though! I'm sure he wants to enjoy as many years there as he can - enjoy success and win trophies.
"He is living the dream so I hope he does that for as long as he wants to do it. If he moves down the line then that's the way football is. That's a decision he will make. He just has to learn the game."
While Tierney has been sensational since emerging onto the scene, there is a very good chance that should he join either of the two clubs that are reportedly after him, he would find himself down the pecking order and may find opportunities are severely limited.
And having already established himself as a key part of the Bhoys' first-team and using that opportunity to make an impression on the international stage, it would surely be a mistake for him to move on now, as McStay suggests, unless one of the interested parties can assure him that regular game-time is something that they can offer.