This summer, Arsenal made five signings - three senior players and two youngsters. But which one has been the best value so far?
Asano was loaned out to VFB Stuttgart, which left four players who could make an immediate impact on the squad.
Of the four, only Mustafi has nailed down a starting spot. He has started each of the four Premier League games he has been available for, as well as both Champions League matches.
The club have gone unbeaten in that spell, winning five and drawing one of those six games, and conceding just three goals.
Despite having had previous success with the Per Mertesacker/Laurent Koscielny centre-back partnership, it has been clear for some time that the towering German's lack of pace is something that can be exploited.
Mustafi has taken his fellow countryman's place in his absence due to injury, but with the way he has been playing, he has no reason to worry about losing it upon Mertesacker's recovery. The new man put in an incredible showing to shackle and frustrate Chelsea's Diego Costa in a 3-0 win for Arsenal, while Mertesacker was sent off for a last-man challenge on the same player last season in a 1-0 defeat.
Mertesacker and Koscielny went unbeaten as a centre-back partnership over two years between 2012 and 2014, and perhaps Mustafi's new partnership with the Frenchman can replicate that success.
What of the others?
While Rob Holding has looked a promising prospect when called upon in the heart of defence, his potential partnership with Calum Chambers (loaned out to Middlesbrough) is very much something for the future.
Lucas Perez scored a brace in his second start for Arsenal against Nottingham Forest, but is being kept out of the team by Alexis Sanchez's improving form as a striker.
Granit Xhaka has been given his chance following Coquelin's injury, and has scored two rockets already, but it is the solidity and consistency of Mustafi's partnership with Koscielny that has been the greatest boost for the Gunners so far, and makes Mustafi Arsenal's best summer signing so far.
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