Arsenal have made few blunders under Mikel Arteta, who has endured plenty of trials during his short spell as a head coach. Dealing with various issues born of previous regimes, the Spaniard was calm and calculated in his decision-making, which culminated in the success they hope to achieve.

However, no manager can get every decision right.

Whether it be a tactical blunder to lose a game, or the wrong substitution to surrender control, arguably few mistakes are as frustrating and long-lasting as selling a player and watching them go on to thrive.

That has certainly been the case with Matteo Guendouzi, who admittedly struggled to outline himself as a star central midfielder for the new boss. It seemed like the 24-year-old remained rash and often thoughtless in his displays, which led to his eventual exclusion from the team.

Former Gunners player Jeremie Aliadiere had suggested that his compatriot hadn't "grown and matured" enough to stake his claim. As was the case with Mesut Ozil and Piere-Emerick Aubameyang, if they did not fit the system, Arteta would let them go.

So, for a fee of just £9m, the Frenchman departed – after being banished from the squad by Arteta.

How much is Matteo Guendouzi worth now?

Having featured 82 times for the North London outfit, his 21 yellow cards during that period certainly support the earlier suggestion of a rash play style.

However, as a youngster joining, Guendouzi came with a big reputation and was expected to be the future of the club's midfield. When he made the final shortlist for the Golden Boy award, this was only further cemented.

Featuring heavily in his first full season, the £41k-per-week stopper acted as a steady presence at the base of midfield. This culminated in an unspectacular 6.79 rating, which would improve just slightly the year following to 6.84. Either way, it marked progression.

However, the eventual sale of such a promising talent was deemed a must to continue progressing as a club, even if journalist Aaron West had suggested there was "something special" about the young destroyer.

Since moving to Marseille, as performances have improved, so too has the valuation of the 6 foot 1 star. Boasting a 7.00 rating last campaign, in which the French international seemed to finally be growing into his potential, CIES Football Observatory clearly took note.

They suggested that Guendouzi's value had rocketed, and from that £9m initial sale the midfielder was now worth €35m (£31m).

At the tender age of just 24 too, this is a figure set to only increase with each passing year of improvement.

As aforementioned, Arteta has not made many errors during his reign. But this decision to offload their former star youngster might well be turning into a mistake.