Arsenal have made their £45million budget stretch this summer.
Nicolas Pépe joined from Lille for a club-record fee, boosting an already impressive forward line containing Pierre-Emerick Aubameyang, Alexandre Lacazette and Mesut Özil. Dani Ceballos signed on a season-long loan from Real Madrid and William Saliba is set to arrive next summer.
The Celtic full-back is having a medical and, if all things come back clear, his £25million move will be completed before the window closes.
On one hand, the fee seems excessive for a player untried and untested outside of the Scottish Premiership. However, it’s potentially not just the bargain of the summer for Arsenal but one of the biggest bargains in the club’s history.
The 22-year-old has over 100 appearances for the Scottish giants, he’s played in Europe for the Bhoys and he’s earned 12-caps for his country. If he stays clear of injuries and develops as expected, the Gunners have a player who can fill the left-back role for the next decade.
Tierney addresses a weakness. In fact, he addresses two areas of weakness in the Arsenal backline. Though primarily a left-back, he can play as a centre-back in a defensive three. That gives Unai Emery the option to change the system mid-game without wasting a substitute.
When you think about it, his versatility means the Gunners are paying £25million for a player who can operate in two, perhaps even three if you include wing-back, roles.
Down the left flank, Tierney is a creative menace. Last season, he put in 4.54 crosses per 90 with over 50 per cent of those finding his target. These aren't just hopeful balls into the area, either. They're often perfectly placed pull-backs or passes to a team-mate.
He averaged 1.46 open-play key passes, showing himself to be handy on the ball for a full-back, and he could strike up quite the understanding with Aubameyang down that channel.
Not only does Tierney add to Arsenal's potency, but he also goes a long way to shoring them up defensively.
If the Gunners have any hopes of qualifying for the Champions League this season, they have to cut the 51 goals they conceded last term by around about 20 per cent.
Though Tierney can't transform the defence single-handedly, he does do a lot of the dirty work others perhaps shy away. Despite playing for the best side in Scotland, and by default the most dominant, he still posted impressive defensive numbers.
No Arsenal defender can match his 2.1 tackles or 4.65 interceptions per 90 last term and if he's able to get close to that at the Emirates then opposition forwards will have a task getting past him. If he shuts down the left side of the defence the Gunners will be able to concentrate their efforts on the right side. It'll be easier to put out fires.
Tierney's arrival isn't as exciting as Pépé's but he could be the most important arrival of the window for Emery.