It didn't take long for the television pundits to identify one of Arsenal's biggest flaws in the 2-1 loss to Newcastle on Sunday.
Shkodran Mustafi's defending for Newcastle's equaliser left a lot to be desired and the BBC's Martin Keown and Sky Sports' Nemanja Vidic -- who both know a fair bit about centre-back play -- didn't hold back in their criticism.
"Mustafi seems to still be making the same mistakes he made earlier this season," Keown said about the German, drawing the same conclusion as many others.
To make his point, Keown highlighted similar mistakes by Mustafi against Southampton and Newcastle as he allowed a player to score after beating him to a cross in both games.
"If we look at last week against Southampton against Shane Long, a little run made to the near post and his body shape was all incorrect, he's not looking at a possible opponent and he gets done at the near post," Keown explained on Match of the Day 2. "The same thing happened again today."
Vidic had similar complaints, and also accused Mustafi of "just looking at the ball" when he allowed Dwight Gayle to run on to a long pass over the top from Jonjo Shelvey in the lead-up to that equaliser.
"If you're a defender you cannot allow yourself to do that. You have to be on your toes and you have to be sideways. In that case, you can run in all directions and you can see what is coming," Vidic said.
"You have to twist your body, look lively. In this situation, you just have to react. He's just looking at the ball, he doesn't know what's going on around him."
It's a damning verdict for a player who is by far the most expensive defender Arsenal have ever bought. But nearly two years after Wenger decided to spend £35 million on the former Valencia player, it's increasingly clear Mustafi has only added to Arsenal's chronic defensive problems rather than solve them.
This is not the first time this season Mustafi's mistakes have cost his team. His weak defending against Sergio Aguero as the Manchester City striker scored the opening goal in the Carabao Cup final stands out as the most glaring, a low point even in a season filled with shake-your-head-in-disbelief displays by the Gunners' back four.
His habit of trying to blame those mistakes one someone else -- the referee for the Aguero goal, the assistant on numerous occasions and Petr Cech for the Southampton howler -- only makes them increasingly frustrating.
It's bewildering how a player can be so inconsistent. Mustafi had a great start to life as an Arsenal player, initially rejuvenating the back four and forming a good partnership with Laurent Koscielny. He was also one of the main reasons that Wenger's switch to a back three worked so well for a while. But he continues to make fundamental errors that an already fragile defence simply can't cope with.
Perhaps it's unfair to put too much blame on Mustafi alone. Koscielny, Hector Bellerin, Calum Chambers, Rob Holding and even Cech have not been mistake-free this season. And fatigue may have been a factor in Sunday's game, with Mustafi having also played the full 90 minutes in Moscow on Thursday night while Koscielny and Bellerin were both rested against Newcastle.
And serious questions must also be asked about the Arsenal coaching staff, who have completely failed to develop a player who was a Germany international when he arrived.
But his struggles highlight how Arsenal need to completely rebuild their defence this summer if they are to get back into the Premier League's top four.
With Per Mertesacker retiring, Koscielny turning 33 in September and young duo Holding and Chambers still developing, it may be tempting for Arsenal to hold on to the only centre-back in the squad who is actually in his prime. Especially since they're unlikely to get their money back at this point.
But it's time to admit that the £35m simply wasn't money well spent, and start from scratch. Arsenal still need a solution to their defensive woes, and Mustafi is not it.