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Not every Arsenal fan will admit to this, but Emiliano Martinez 's departure last summer was a mistake in every sense of the word.
The keeper joined Aston Villa for £20million after his impressive end to the season with the Gunners as he starred in place of the injured Bernd Leno including a memorable FA Cup victory.
The general consensus was the Argentine had shown more than enough to keep the No.1 jersey when the German international returned to fitness, or at the very least, given the chance to fight for it next season.
But instead, they decided to sell Martinez while his stock was perceived to be at it highest, with Mikel Arteta sticking with Leno.
Unfortunately for Arsenal, Martinez's stock has only continued to rise since his move to Villa Park.
Emiliano Martinez had an impressive debut season with Aston Villa
(Image: Getty Images)
Should Arsenal have kept a hold of Emiliano Martinez last summer? Comment below
The 28-year-old was arguably the best keeper in the Premier League last season and helped turn Villa from a side that narrowly escaped relation the previous (with one of the worst defences in the league) into a team that looks rigid at the back and would have likely secured a top-half finish if it wasn't for the injury to Jack Grealish.
It's been a remarkable turnaround and Martinez deserves credit for shoring up what was an incredibly leaky defence that shipped 67 goals last term.
Martinez secured 15 clean sheets in 36 Premier League appearances for Dean Smith's side conceding just 44 goals in total – despite him being one of the division's most-worked stoppers.
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On the face of it, it seems ridiculous to suggest selling your back-up keeper for £20m is a mistake, but that's how good Martinez has been since.
There is no doubt it was a difficult decision for Arteta to make.
After all, Leno has been one of Arsenal's most consistent performers since arriving from Bayer Leverkusen whereas Martinez's success last term was only a small sample size.
But, in hindsight, the North London club may have been too hasty to make that call as Martinez has taken his game up an extra notch and is operating at a higher level than Leno right now – while there are big questions over the German's future.
Now, events of this week have seen the decision to sell Martinez actually backfire in more ways than one.
The Villans have usurped Arsenal to the signing of Emi Buendia, who joins the Midlands side for £35m from Norwich City.
The Argentinian was one of Arteta's top targets this summer as he looks for another creative midfielder – with Martin Odegaard's future at Real Madrid up in the air.
And Martinez has played a major part in convincing his international teammate to link up with him at Villa Park.
While Villa made major advances to the player, convincing him of their plans for him and the side, and showing greater desire to get him, Martinez has also been working on Buendia while on international duty; as he stated on one social media post, it's been 'Agent Martinez' indeed.
Emi Martinez has played a key role in Buendia's move
This is potentially a massive own goal by Arsenal.
In short, a former player (who they arguably shouldn't have let go) has ended up playing a role in persuading one of their transfer targets to join the club they sold him to.
There's no way that anyone could have predicted this happening, but it's certainly more ammunition for those that believe Arsenal should have kept a hold of Martinez – and undoubtedly a sore one to take for the club.