Arsenal manager Arsene Wenger is keen to cure the club's complacency that led to the collapse against Anderlecht rather than improve his defensive options in the January transfer window.
Mikel Arteta, Alexis Sanchez and Alex Oxlade-Chamberlain's goals had the Gunners coasting towards the knockout phase with 29 minutes remaining at the Emirates Stadium before the Belgian side launched a stunning second-half comeback.
Anthony Vanden Borre's double and Aleksandar Mitrovic's 90th-minute header secured a point for Anderlecht to keep alive their hopes of reaching the last 16 and leads to further questions over Arsenal's defence, which sees Wenger with just six players capable of playing at the back.
Injuries to Mathieu Debuchy and Laurent Koscielny have further reduced the options available to Arsenal but Wenger is unwilling to contemplate signing defenders in the new year and instead wants to look at the reasons behind the side's latest troubles.
Asked whether he plans to sign defenders in the January transfer window, Wenger responded: "Honestly it's not the worry tonight. We just came out of two clean sheets and maybe thought we had got the job done at 3-0.
"The target is to go to Swansea with another [good] defensive performance. I also believe the luck we have is that we still have a good chance of qualifying.
"If we had lost tonight, what could have happened, would have been a very bad situation for the qualification. For winning the group, tonight you can say that's nearly impossible now."
Bacary Sagna, Thomas Vermaelen, Johan Djourou and Ignasi Miquel all left Arsenal on a permanent basis during the summer with Debuchy and Calum Chambers the sole defensive additions, transfer business masked by the marque additions of Sanchez and Danny Welbeck.
Though Arsenal are second in Group D with a five-point cushion, their hopes of qualifying top ahead of Borussia Dortmund and being seeded for the knockout phase have all but been extinguished by Anderlecht's late comeback.
The club have been knocked out of the Champions League in the last 16 stage in each of the past three seasons in which they have failed to top their group and could now face the likes of Real Madrid or Bayern Munich come the knockout phase.