Mertesacker says the team were disappointed with their display at Emirates Stadium.
"We have had a difficult week, our results were kind of an accident, now we have to find our game again," the defender told arsenal.com. "The international break was kind of a killer for us. We have to find our strength again quickly.
"We have the potential in us, but first we have to fight. We have to learn quickly from what happened [at Norwich last weekend] and against Schalke. If we do not find these solutions, it is going to be difficult in the Premier League and the Champions League.
"It is our task now to find our self-confidence, we have great players with great potential. So it will be good to have a game in three days so we can show our potential again.
"We will try to be positive before the next game. In our training sessions we will look to get our confidence back. Sometimes you need one game to find your strength and quality, so let's do it on Saturday."