As Cristiano Ronaldo’s shot squirmed in for Portugal under David de Gea in Sochi on Friday , it must have been a relief to fellow goalkeepers. Even someone like the Spanish number one, so often placed in the world class bracket for his position, will occasionally make an error.

It should have been comfort for Bernd Leno at least.

Nearly a year to the day also in the Fisht stadium in Sochi, he made a similar mistake to de Gea. In Germany’s opening group game of the Confederations Cup, Australia equalised after Leno did not get down quick enough to Tom Rogic’s shot, which travelled underneath him.

Germany did win 3-2 but Leno made another error which led to a goal in the second half, with the ball this time slipping from his grasp after a free kick. To date, that remains the penultimate game he played for Germany, with Marc-André ter Stegen playing the rest of the tournament.

The 26-year-old still made Joachim Löw’s provisional squad for the current World Cup but lost out to Kevin Trapp in the race to be third choice.

And yet, whilst his stock in Germany isn’t all that high right now, Bernd Leno has the potential to become a very good signing for Arsenal.

Bernd Leno lets the ball through his grasp in the Confederations Cup (Getty)

To explain why, you first have to go back to just before the 2014 World Cup when Leno had just finished his third season at Bayer Leverkusen.

Over the course of those three campaigns, you only needed one hand to count his mistakes.

That was reflected in him topping kicker magazine’s rankings as the Bundesliga’s best goalkeeper at the end of his first season in 2012 and then again in 2014.

That only came after something of a freak breakthrough. With both Leverkusen’s first and second choice goalkeepers injured one game into the season in August 2011 they loaned a 19-year-old Leno from Stuttgart where he had been third choice.

Within a month, he’d kept clean sheets in his first three games and become the youngest ever goalkeeper at the time to play in the Champions League.

Back then, Leno told BILD in Germany that Jens Lehmann had been his mentor at Stuttgart. There’s a certain irony then that on the day Leno should join Arsenal, Lehmann announced his departure from the coaching staff earlier in the day.

Leno is prone to an error (Getty)

Much like Lehmann in his prime, Leno developed a knack for being a player who could win his side points - more so then than now. In the 2013/2014 season, he even developed the nickname “Elfmeter Killer” literally “penalty killer”, saving six penalties across the campaign.

In hindsight, that summer was when things changed for Leno as Leverkusen appointed Roger Schmidt as their new head coach. That changed how they played, the focus of which was a more gung-ho style of pressing and little emphasis on building up from the back.

The tactic proved effective in spells but the longer that Schmidt stayed, the more apparent a decline became. It’s difficult to recall when Schmidt’s Leverkusen ever really had a Plan B and his reign came crashing down with a 6-2 defeat at Dortmund in March last year. “A step in the right direction,” was how Schmidt bizarrely termed it in the press conference, with Leverkusen involved in an unfamiliar fight against relegation for the rest of the season.

How the time under Schmidt affected Leno could be seen by his comments in November. Under new coach Heiko Herrlich, they were looking a lot more effective without getting the rewards which they would later in the campaign, as they narrowly missed out on Champions League football.

“I am very happy with the way that we try to play football,” said Leno, pulling back for the punchline.

“For three years, we had no build up play. The coach now puts more of an emphasis on build up play and possession – I think that’s very, very important.”

Roger Schmidt's style of play at Leverkusen left Leno exposed (Getty)

Under Schmidt, Leno had to fend for himself more, both on the pitch and in training. There were times when he rarely had proper goalkeeping training with the goalkeeping coach, according to sources close to the club.

In games, large amounts of space were left behind the Leverkusen backline and Leno struggled to adapt to sweeping duties, with similar mistakes recurring in each Bundesliga season with Schmidt.

In the 2014/2015 season, he came for the ball at home to Paderborn and away in Hamburg but was too late on both occasions. The following campaign, he did the same at Dortmund before a home game against Augsburg produced the most calamitous error of his career.

After being rolled a simple back pass, Leno swung for the ball and missed, leaving the ball to tantalisingly trickle in to an unguarded net. “A complete blackout from me,” as he put it at the time.

Wind forward another season to September 2016, having gone to the Euros that summer with Germany. Leverkusen announced shortly before kicking off at home to Hamburg that Leno had extended his deal at the club. Even if there was friction with Schmidt, Leverkusen were still playing in the Champions League at the time. The day though would be marked though once again by Leno haring out for a ball that wasn’t his, allowing Bobby Wood to round him and tap into an empty goal.

It seems little coincidence that those mistakes, which always occurred near the beginning of a season, would weaken Leno’s confidence. The remainder of those campaigns always included a couple of handling errors, whether it was parrying out softly to opponents or the ball squirming underneath him. The knock-on effect was visible but so has been the improvement in his performances again since Herrlich took over last summer.

Bobby Wood profits from a Leno error to score for Hamburg (Getty)

Sure, there were still two occasions in the most recent season, against Hertha Berlin and Cologne respectively, where Leno was caught out after racing off his line once again. The handling errors were fewer however.

That Joachim Löw has still had him in contention for the Germany squad in recent years tells you that despite the increase in mistakes, he’s still been holding a good level in the Bundesliga. It just doesn’t quite compare with the one after breaking through.

At penalties for instance, he’s lost his touch. Ever since the sixth and final penalty save he made in the 2013/2014 season, Leno has stopped just one of his next 27 spot kicks.

Bernd Leno joins Arsenal from from Bayer Leverkusen (Getty)

Leno though is likely to benefit from a fresh start after over 300 Leverkusen appearances in total. Another step in Germany would have been sideways. Even if Leverkusen are playing Europa League football next season, Arsenal is a bigger club and challenge for Leno.

Having a core of German speaking players like Granit Xhaka, Shkodran Mustafi, Mesut Özil and Sead Kolasinac should help him to settle in, let alone also having Per Mertesacker there, even if he’ll be working as the club’s academy manager.

Most important for Leno is that he’s able to adapt to however Unai Emery style of play.

It shouldn’t be forgotten that it took even someone like David de Gea time to adjust and indeed time to build up to the world class goalkeeper he is seen as today.