The 22-year-old joined the Gunners for £25m on a hectic transfer deadline day, giving him hardly enough time to make peace with his departure from Celtic Park.
Yet, due to his current injury keeping him out of Arsenals 1-0 win over Newcastle in their Premier League opener, he was able to spend some final time at his boyhood club over the weekend, according to former boss Neil Lennon.
As reported by The Sun, Lennon spoke of what occurred when the young left-back came back to the training ground.
"He popped in and everyone was delighted to see him," Lennon began. He got a nice farewell from the players and it was emotional for him.
"But the players will get on with it now and thats what you do, you roll on. Hes going to be a big miss obviously but theres an opportunity there for someone else to take on the mantle now."
The Suns report continued with quotes from Tierney - who revealed that making the move was a tough decision, but ultimately an opportunity he couldnt afford to pass up.
Tierney said: “It was the hardest decision in my whole life that Ive had to make. I had to speak to my family and my close friends and my agent as well because its a hard decision to leave a club that you love so much. People need to know that as well.
“I feel Arsenal is a massive club and its a great opportunity for me as well. Im delighted to be here."
Arsenal fans will have to wait to see their new man in action, though, with the Scottish defender currently recovering from a double hernia operation that took place over the summer.
Tierney was quick to alleviate any concerns from supporters, suggesting that hes edging closer to full fitness each day.
“I’m just getting back fit now," he added. "Im just getting back involved with a ball and back running. So hopefully its not going to be too long.”