Premier League club's worst signing of all time.Gary Neville, who worked with Mustafi at Valencia in 2016, claimed the club desperately tried to offload the defender but could never find a buyer for him - that's how bad he was.Naturally, the Spaniards couldn't believe their luck when Arsenal offered a £35 million for him two years later.The error-prone German was not only predictably disastrous for the Gunners, but he somehow stayed in the first team for three straight years before eventually being shipped out to Schalke.Arsenal finished outside the top four for the first time in two decades at the end of Mustafi's first season, and they haven't returned since.
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