Kieran Tierney will be a “sensation” for Arsenal, says Celtic legend Davie Hay, with the Gunners considered to have landed themselves a bargain in a £25 million ($30m) transfer deadline day deal.After several weeks of speculation regarding the 22-year-old full-back, he was finally prised away from Parkhead before the summer window slammed shut in England.Celtic had been understandably reluctant to part with a prized asset, with an academy graduate having flourished after stepping onto a senior stage in Glasgow. Article continues below Editors’ Picks Emery out of jail – for now – as brilliant Pepe papers over Arsenal’s cracks What is Manchester United’s ownership situation and how would Kevin Glazer’s sale of shares affect the club? Ox-rated! Dream night in Genk for Liverpool ace after injury nightmare Messi a man for all Champions League seasons – but will this really be Barcelona’s? Hay, though, acknowledges that the lure of the Premier League was always going to be too great, with Tierney now ready to show a wider audience just how good he can be.The Hoops icon told the Evening Times: “The moment Kieran Tierney burst onto the scene four years ago as a 17-year-old, which is when he made his debut, and who played as if he was a seasoned pro, I quickly concluded that one day a club from a bigger league, and importantly with a lot of money, would come in with a record bid.“It didn’t take long for most of us to realise the Celtic had produced a real gem. The best we’ve seen in a long time. That this was a lad who could play anywhere he wanted. Keeping Tierney a secret was never on the cards.“Arsenal bid £10million for him when he was 19. That was knocked back. They were never going to go away forever. Everton had a nibble a year ago. God knows how many other clubs have sent a scout to Celtic Park“KT was always, one day, going to say his goodbye to the club he will always support to go on an adventure.”Hay added: “Arsenal have done well to get him for £25million and I’m sure most Celtic supporters, while disappointed, understand why one of their own is now an English Premier League player.“How good is he? I was fortunate to play with Tommy Gemmell and Danny McGrain. I have no hesitation putting young Kieran in that bracket in terms of the great full-backs produced by Celtic.“My guess is that Tierney didn’t want to leave Celtic. There was no banging on Neil Lennon’s door, he didn’t put in a transfer request and never once spoke about playing elsewhere.“However, some opportunities are too good for anyone to turn down.“Arsenal haven’t won so much in recent times; however, we are talking about a huge club in a fantastic league, and it’s a team which I believe is getting better.“I have no fear about Tierney being good enough. He is going to be a sensation.”Tierney will be hoping to make an immediate impact in a new-look Arsenal side, with it possible that a number of fresh faces will line up for the Gunners in their 2019-20 season opener away at Newcastle on Sunday.