The 25-year-old German posted an apology on his Facebook account for the tame penalty miss in the Champions League last-16 first-leg tie against Bayern Munich at the Emirates Stadium on Wednesday night.
It proved a costly error as the soft, chipped effort in the eighth minute was saved by Manuel Neuer - his childhood friend - and the Bundesliga giants went on to win 2-0 after Arsenal goalkeeper Wojciech Szczesny had been shown a red card for tripping Arjen Robben.
Ozil has polarised opinion with a string of inconsistent displays since a club-record £25million signing from Real Madrid on deadline day in September.
Mertesacker, though, maintains his countryman just needs time.
"We have a lot of games here in England and everyone is tired, but it is not just up to Mesut," said Mertesacker, who himself has developed into a consistent performer for Arsenal following an underwhelming start at the north London club after signing from Werder Bremen in August 2011.
"It is up to everybody to encourage and come back, during the game we all need to encourage each other.
"Mesut has played a lot of games and he is a massive player, we need him at his best. Game by game, he will come back stronger.
"It is not normal to come here and perform well in the first season over 50 games.
"Mesut is very important for us and he is a very creative guy. We need his assists and his goals, so the best is to encourage him."
Ozil found himself berated by team-mate Mathieu Flamini during the second half in an attempt to lift the German's work-rate.
Mertesacker feels that is a positive trait of Arsene Wenger's squad.
"It is good we encourage each other and we have to do well as a team. Talking to each other is the best thing we can do," he said.
"we need everyone on the pitch with their full mental strengh.
"Mathieu tries to keep everyone alive and that is massive for the team, so I would not assess that as an argument.
"It is good to show everyone we are ready for the fight."
Arsenal can retain some slim hope of an unlikely comeback given their 2-0 win at the Allianz Arena last season, which saw them exit only on away goals.
However, there is no escaping the obvious disappointment of a missed opportunity to have put the European champions on the back foot.
"It was (a missed opportunity) and we saw a chance to really compete at that top level," Mertesacker said.
"With our fans and our spirit we could have scored, but afterwards we dropped a bit and are disappointed.
"But we will go to Munich and have nothing to lose, it is the same as last year."