It is a measure of William Saliba's defensive ability and physical power that his Arsenal team-mates have now stopped bothering to even challenge him in training.
"No one goes past him," said Ben White, the Arsenal right-back, in an interview with former goalkeeper Ben Foster last week. "No one even tries. There is no point."
Across the Premier League, there must be many forwards who would agree with White's assessment. Saliba is perhaps the most physically dominant defender in the division, a 6ft 4in giant who moves like a sprinter but turns like a dancer, and he is formidable in one-versus-one battles. "Absolutely incredible," said White.
In usual circumstances, Saliba's extraordinary skill set represents one of Arsenal's most important advantages.
Who else can defend so comfortably in a high line, move so elegantly on the ball and also dominate the aerial battles in his own penalty area? In the Premier League, perhaps only Virgil van Dijk offers the same blend of poise, power and pace.
The occasional problem with Saliba's brilliance, though, is that there is no one else like him in the Arsenal squad. Mikel Arteta has built a system in which Saliba is absolutely fundamental.
And so, when Saliba is out, as he is against Van Dijk's Liverpool this weekend, there is simply no other player who can offer the same breadth of attributes.
A long time has passed since Arteta has had to deal with this particular headache, as Saliba played every single minute of Arsenal's Premier League campaign last season - becoming the first outfield player to do so for the club.
The last time Arsenal were without him for a league match was in the spring of 2023, and on that occasion his absence proved to be disastrous.
The loss of Saliba to a back injury was undoubtedly the most significant factor behind Arsenal's inability to win the title race against Manchester City.
This might all sound a little hyperbolic. Arsenal supporters would rightly argue that they are far from a one-man team. But there is hard and compelling evidence to prove the point of Saliba's paramount importance to Arsenal's evolution in recent seasons.
Not only is Saliba statistically the most effective player in this current Arsenal team, he is also statistically the most effective player in the club's entire Premier League history. Not even the likes of Tony Adams, Patrick Vieira and Thierry Henry can match his return of 2.36 points per game in his Premier League career.
Kai Havertz, Saliba's current team-mate, has also won 2.36 points per game in an Arsenal shirt, but his body of work is far smaller: he has played 45 league matches for Arsenal, compared to Saliba's 73.
There's more. Since the start of the 2022-23 season, Saliba's first in the Premier League, Arsenal have won 74 per cent of their league matches with him. In the 11 games without him, their win percentage plummets to 46 per cent. With him, they concede an average of 0.8 goals per game. Without him, that number doubles to 1.6.
Saliba is not an obvious leader like Gabriel Magalhaes, his chest-thumping defensive partner, or club captain Martin Odegaard.
Behind the scenes he is known for being almost comically laid-back at times, and you will not catch him shouting and screaming. When he was sent off against Bournemouth last weekend, his face was expressionless as he quietly plodded down the tunnel.
But he is evidently a leader in a footballing sense, because so much of what Arsenal do is made possible by his presence. Saliba has quite literally transformed the shape of the side. After Saliba came into the team, Arsenal's defensive line pushed an average of two metres higher up the pitch
The big question, then: what on earth do Arsenal do without him? The good news is that Arteta has more options in his squad than he did in 2023, when Rob Holding struggled to fill the void left by Saliba. The bad news is that his backline is currently plagued by injury problems.
If everyone was fully fit, the replacement for Saliba would be Jurrien Timber.
But Timber is not fully fit, and has not played since a muscular injury forced him off against Paris Saint-Germain on October 1. It remains to be seen whether he is ready to feature.
The Dutch international can play either as a centre-back or as a right-back, allowing White to move into a central position.
Another option would usually be new signing Riccardo Calafiori, who could shuffle inside from left-back. Except Calafiori is also dealing with an injury after twisting his knee in midweek. Just as Saliba needs replacing at centre-back, Calafiori likely needs replacing at left-back.
Takehiro Tomiyasu can play in all four defensive positions, but he is also injured again. Kieran Tierney, meanwhile, remains unavailable because of the serious injury he suffered at the European Championship. Everywhere Arteta looks, he must see problems.
Even if Timber is fit to play as a centre-back, the left-back issue still requires addressing. Oleksandr Zinchenko has struggled in the past against Mohamed Salah and has not played since August because of injury, while teenager Myles Lewis-Skelly is hugely promising but only 18.
This might be a situation that requires some creative thinking. One option is to include the unspectacular Jakub Kiwior as a centre-back alongside Gabriel.
Another is to play midfielder Thomas Partey as a right-back, with White coming into the centre.
It felt telling that Arteta put Partey into a right-back position for the second half against Shakhtar Donetsk on Tuesday.
Perhaps the boldest of all options, though, would be to temporarily convert Declan Rice into a central defender.
Arteta has briefly used the England midfielder there before, in an experimental way, and it is possible - albeit unlikely - that he would consider this the time to activate his ultimate emergency plan.
It all makes for a brutal examination of Arsenal's squad depth, and indeed their medical department.
The absence of Martin Odegaard and Bukayo Saka has already presented significant hurdles for Arteta this season, but the loss of Saliba - even for just one game - provides the biggest obstacle of all.
These are early days in the season but it already feels like a major test, and one that Arsenal must pass if they are to win the Premier League.