He wasn't short of critics during his time at Parkhead.

Whether it was strict diet plan or the fact that Aberdeen managed to run his team agonisingly close in the title race, ex-Celtic boss Ronny Deila got a lot of stick during his time in Glasgow.

But one thing that has perhaps been glossed over by many fans of a green and white persuasion is that the Norwegian spotted a raw young talent in the Hoops youth team that he reckoned was destined for bigger things.

So it's no surprise to the former boss that Kieran Tierney has become Scotland's most expensive player after his record-breaking move to Arsenal this summer.

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"People did not want to play against him [in training]", Deila said, speaking to the Telegraph.

"He was so aggressive.

"His attitude was maybe the best I have ever seen."

Tierney's attitude may have been what brought him to the dance at Celtic Park back when he was just 17-years-old under Deila.

It's his talent and work ethic that has kept him there.

And Deila believes the left-back can go on to the very top as a superstar - just like former teammate Virgil Van Dijk - because he has that special ability.

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Deila added: "I am not scared of him going to Arsenal — he will adapt to the top level of the Premier League very quick, I’m sure.

"I am as sure as I was with Virgil van Dijk that he is going to make it.

"To take it to the highest level you need something special and these players are special."