Tierney, 20, has been tipped as one of the most exciting young prospects in Scottish football.
The player would cost around £25m for his services, with Hartson suggesting that Manchester United could be the young full-back’s next destination.
“I’m hearing he’s Manchester United’s number one target,” Harston told the BBC’s Scottish Football Podcast. “But why on earth would Brendan Rodgers sell Tierney right now?
“If I’m Brendan Rodgers, I’m saying to [Jose] Mourinho, ‘Let him have another season here, keep your £25-30m for now, he’s got Champions League football, he loves playing for Celtic.”
Harton himself was quick to also suggest that the player would benefit from holding off on a move to United so early in his career: “Give him another year, 18 months at this level until he becomes more of a man, more established, more mature physically, then in 12-18 months’ time, there is no doubt Kieran Tierney will go on and play for one of the top three or four clubs in Europe.
“I have every confidence in Kieran Tierney to become a top, top player. He is a great player now, but he can only get better.”
Do Manchester United need another fullback?
The emphasis has been focused on United adding a winger to their ranks this transfer window. Ivan Perisic is, of course, the name we’re all used to hearing by now, with Thomas Lemar being linked more recently.
The left fullback position is not a position United are particularly short on. Dailey Blind has slid into the left-back position so far this season, starting there on both of United’s opening games of the season. Mourinho has also reportedly been pleased with Luke Shaw’s progress this summer, following an ankle ligament injury he sustained in April.
Shaw has struggled with injuries since his move to Old Trafford.
Should Shaw and Blind become unavailable over the course of the season, Ashley Young has also filled in on occasion as left-back in recent years as well. Whilst the left-back position may not be a priority for United at this moment, Tierney’s natural ability is undeniable and looks like he could be the real deal. It would make sense if United – along with several large teams across Europe – were motoring the youngster’s progress this season.