The Gunners were 2-0 winners against Monaco at Stade Louis II thanks to goals from Olivier Giroud and Aaron Ramsey.
We had one bad game and that is enough to get knocked out
However, Arsenal couldn’t find scored a third goal which would have successfully overturned their 3-1 first-leg deficit.
Meretsacker, who was largely culpable for their horror showing at The Emirates, questioned the north London side’s mentality in the first leg.
“It is difficult after such a performance like that to think, ‘yeah, we missed that’,” Mertesacker is quoted as saying by London Evening Standard.
“In the first game, we didn’t have that mental level you need to compete at the highest level. That was missing but you could see last night how good we are as a team and how well organised we can be.
“We need to consider that every day in training and in games. That is why we are so far away from winning the Champions League.
“When you get knocked out, you are far away. It is the last 16 and Monaco were underestimated by a lot of people but they deserved it by playing well in the first leg. We had one bad game and that is enough to get knocked out.
“In the first leg, we conceded that late goal which was overall the killer but last night we didn’t look back. We just tried to do our job well. That was the first target — to not look back and think, ‘what have we done wrong’, especially the first leg, so it is really disappointing for us.”
Olivier Giroud broke the deadlock against the Ligue 1 side in the 35th minute before Aaron Ramsey doubled the away side’s lead with 12 minutes remaining.
Arsenal have failed to get past the Champions League last 16 in the last five years after defeats by Porto, Barcelona, AC Milan and Bayern Munich (twice).
The Gunners are in third place in the Premier League table and are set to face Bradford City in the FA Cup semi-final at Wembley.
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