William Saliba went down in Dallas on 14 July, during France's World Cup semi-final against Spain, and the picture that ran everywhere afterwards showed him leaving the pitch with the flat, careful walk of a man who already suspects the diagnosis. It was a back injury, surgery followed, and the first word out of England was five months. Sami Mokbel of the BBC later revised that downward, saying two to three months on the Daily Grind after a successful operation, which is the kind of news a club is grateful for and still has to plan around, because nobody builds a title defence on the word "fortunately."

Arsenal's answer arrived on 20 August: Ezri Konsa, from Aston Villa, for a fee reported at £51m, or €59.6m depending on which currency and which add-ons you believe. He is twenty-eight, comfortable at right-back and centre-back both, and Transfermarkt has his market value at €45m. That is a gap of roughly £13m between what the site's algorithm thinks he's worth and what Arsenal actually paid, which is not scandal, just the going rate for buying in August with your first-choice centre-back already in a scan and your first-choice right-back, Jurrien Timber, also unavailable. Villa were selling for reasons that had nothing to do with sentiment. The BBC's coverage of the deal spent more time on Uefa's squad cost ratio rules than on Konsa himself, which tells you Villa's need to sell mattered as much as Arsenal's need to buy.

The case for Konsa is not hard to make and deserves making properly rather than waved through on the way to a verdict. He has started regularly in the Premier League for six seasons, plays two positions competently rather than one brilliantly, and gives Arteta a squad that can survive a Timber injury and a Saliba injury landing in the same window without pulling teenagers into Champions League football before they're ready. Arteta had already tried Christian Mosquera, Gabriel and Piero Hincapié together in preseason friendlies, and if that trio had looked like an answer, Arsenal would not have spent £51m confirming it wasn't.

That is the detail that undercuts the tidier version of this story. Konsa was signed after an audition, not instead of one, because the audition told Arteta something he didn't want to hear about Mosquera and Hincapié at this stage of their development. That is a reasonable, even sensible piece of squad management. It is also an admission, made without anybody saying it aloud, that the depth Arsenal thought they had going into the season wasn't there, and that the fix for it is a very good defender being asked to do a job he has never done at this level, for this club, against these opponents.

Saliba's importance to Arteta's team was never simply that he defends well, though he does. It is that he is comfortable receiving the ball under pressure from a high line, breaking it with a first pass rather than a hopeful one, and doing that specifically against sides who press you into mistakes for a living: City, Bayern, the two or three Champions League nights a season that decide what your year was. Konsa built his reputation in a different system, at Villa Park, in a team set up under Unai Emery to sit deeper and defend more territory than it invites pressure onto. That is not a criticism of Konsa. It is a description of two different jobs that happen to be filed under the same position.

Arsenal face Manchester City in the Community Shield on the far side of this transfer window, and it is as good an early instrument as any for measuring the gap between what was bought and what was needed. Not because Konsa will necessarily struggle in it. He may well be excellent, on the day, in the way good players often are when the stakes are still relatively low.

It's the pattern across the season that will tell the real story: whether Arteta trusts Konsa in the moments that used to belong to Saliba, receiving on the half-turn with City's front three closing him down, or whether he restructures the whole defensive shape to protect a very good centre-back from being asked to be a slightly different one.

That restructuring, if it comes, will be presented as tactical evolution. It will actually be an adjustment made necessary by a signing that solved a numbers problem without solving a profile problem, a distinction easy to lose in August, when what everyone wants is a name and a fee and a headline that says the gap has been filled. The gap in the squad list has been filled. Whether the gap in the team has been is a different question, and Arsenal will get their first real evidence of the answer against the champions, in a one-off match that decides nothing and reveals quite a lot.