As reported by The Daily Mail, Manchester United are showing significant interest in Celtic's popular young defender Kieran Tierney.

What's the story?

Tierney has made himself a very popular man over the last two years at Celtic, making the left-back position his own and generally being one of their top performers. That's now attracting interest from the biggest clubs around.

That's according to The Mail anyway, who say that Manchester United have sent their top scout Marcel Bout to check on his progress and he is set to take in this weekend's Hearts game too.

The paper reckons Tierney would be available for a few upwards of £10m but a fee in that ballpark is small change for United these days, enjoying the massive boost in TV revenue in English football over the last few years.

Is he the left-back they should be investing in?

The finished product?

At just 19 years of age, Kieran Tierney has a lot of learning to do in the game to become the player he can. However, even at this early stage of his career he's performing to a standard high enough to compete in the UEFA Champions League and at international level.

This season he's performed very well against the likes of Manchester City and just this past weekend put in a great performance for Scotland against Slovenia, despite having to switch flanks and move to the right hand side.

First team football is suiting him well right now and you'd imagine he wouldn't want to give that up, so perhaps it's not just cash Man United have to invest in the youngster but time, patience and faith.

He's played just 66 professional games for his club so far and those appearances would need to continue so his progress doesn't stagnate.

What's sure though is that if he keeps on the trajectory he is currently on, the sky is the limit be it at Celtic, Manchester United or anywhere else.

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