Wenger's Arsenal struggle to make a case for defence
Per Mertesacker maintains the whole Arsenal team must take collective blame for failing to hold onto a 3-0 lead against Anderlecht which blew chances of early qualification for the Champions League knockout stages.
The Gunners looked to be cruising towards the last 16 after Alex Oxlade-Chamberlain added to first-half goals from Mikel Arteta, a penalty, and Alexis Sanchez, who netted another superb goal after his initial free-kick was blocked.
However, any hopes of perhaps overhauling Group D leaders Borussia Dortmund, the next European visitors to the Emirates Stadium in a fortnight, were extinguished as Arsenal hit the self-destruct button in allowing the Belgians to recover.
Anthony Vanden Borre, once of Portsmouth, started an unlikely fightback when he slotted in - with more than a hint of offside - just a couple of minutes after the match looked done at 3-0, before rolling in a penalty to set up the grandstand finale as the Gunners appeared shell-shocked.
Mertesacker was unable to prevent Aleksandar Mitrovic heading in a stoppage-time equaliser at the near post, but the big German centre-half insists defending is not just all about the last line of defence.
"That was a good warning that everyone should raise their game and give maybe 10% when it is needed," said Mertesacker.
"When we drop sometimes everyone has to be involved to defend. You can't afford for just five or six players to defend, or just the back four. That is what we lacked especially in the final third and in the last 20 minutes.
"We have to defend better as a team. We did not stop them playing and they are good at it.
"We still have a comfortable situation in terms of going through.
"We want to secure second place and we still have a big advantage after four games."