There was much excitement among the Gunners supporters when Arsenal spent big to sign Mustafi from Valencia in the summer of 2016, with the Germany international having established a reputation as one of the best defenders in Spanish football.
However, since arriving at the Emirates Stadium, Mustafi's form and confidence have gradually seeped away. The man himself has told Arsenal Player how he's sought to block out the criticism he's been on the receiving end of on social media:
"Social media is difficult to handle when things are going well and then when things are not working out it's even tougher."
"... Then when things aren't going well, obviously you don't like the stuff you read. You don't agree with a lot of comments, so it makes it difficult. It's so much easier when things are going well because when you're reading comments you don't like, you have to go out and play and you've got those comments in your head.
"I managed to try to block it out a little bit. I was not that active on social media and wasn't reading comments, I wasn't too concerned about social media, I just wanted to go back on the pitch and give everything because I knew that in this moment I was not playing the football I know I could play."
Mustafi has fallen down the pecking order at Arsenal this season, making just one Premier League start.
In the recent 2-1 defeat to Chelsea, the centre-back allowed Tammy Abraham far too much time to turn in a dangerous area:
Overall, the signing of the Germany international has been a huge disappointment for the Gunners:
The manner in which Mustafi's stock has fallen is remarkable, especially when considering he was an elite defender in Spain and part of Germany's successful FIFA World Cup squad in 2014.
Over the last couple of seasons, Mustafi has been frequently linked with a transfer away from Arsenal, although the contract he penned upon signing for the club doesn't expire until the summer of 2021.
However, speaking about the defender, new Arsenal manager Mikel Arteta said he's willing to give all players in the squad an opportunity:
Simon Collings @sr_collings
Arteta on if Mustafi has a future at Arsenal: "I told everybody from day one, ‘It is up to you guys . . . you show me how much you want it, you show me you are committed here, you are going to have a chance and it is going to come this week, next week or the following one’."
Even so, with Mustafi there's a sense that too much water has gone under the bridge and a transfer would be to the benefit of all parties.
The Gunners are not blessed with high-class centre-back options, and Calum Chambers has been ruled out of the rest of the season due to injury. However, if Mustafi was going to turn around his fortunes in north London, he possibly would have done so already.