FORMER Celtic hero Kieran Tierney admits crossing swords with Brazilian wonder-kid Gabriel Martinelli in training was a wake-up call as he tried to make his mark at Arsenal. 

The Scotland internationalist joined the Gunners in a £25 million deal last summer and, after shaking off a serious hip injury, made his debut against Nottingham Forest. 

Tierney went on to make 11 appearances before succumbing to another set-back in December - suffering a dislocated shoulder - and lined up against the likes of Liverpool, Crystal Palace and Southampton. 

However, he has revealed that the competition on the training pitch is just as tough as anything he found on match-days. 

Glasgow Times:

Martinelli, 18, has been Arsenal’s breakout star this season, notching 10 goals in 26 outings including a solo wonder-goal against Chelsea in January, and Tierney was given an early introduction to his quality. 

Asked who was the player he was most impressed by during his first training sessions, Tierney said: “Gabriel Martinelli. When I first did a full training session with the team I was put up against him and the intensity of his play was honestly mind-blowing. 

“I thought to myself: this is the standard I need to be at to play for Arsenal.

“I think his hunger and drive and his talent together as one is more than enough to be a world class player for many years.”

Meanwhile, Tierney admits that he misses ‘everything’ about Celtic following his departure after 14 years at the club, acknowledging that leaving was the hardest decision of his life. 

However, the opportunity to test himself at Arsenal was too good to turn down. 

He continued: “I would say leaving Celtic was the hardest decision I'd ever had to make and I knew I would always miss Celtic no matter what happens in life. But the chance to play for Arsenal was a challenge that when I heard of it, I was just looking forward to it.

Glasgow Times:

“I miss everything about Celtic and I always will. I am very grateful for every second I spent playing for the club.”

In a Q&A session with Arsenal fans on Reddit, Tierney also opened up on what delicacies he has missed since making the switch south of the border. 

He added: “My mum brings me Scottish food down, so the main thing would be the square sausage. It's probably that. 

“But just being away from my family and friends is probably the hardest part. I'd been with my parents and seen those people every day of my life and then to come down here away from that at first was tough.”