The Gunners lost 1-0 at Norwich City in the league last weekend prior to last night's 2-0 home defeat at the hands of Schalke in the Champions League and the German centre-back wants a positive response when QPR come to the Emirates on Saturday.
"We have had a difficult week, our results were kind of an accident, now we have to find our game again," said Mertesacker.
"The international break was kind of a killer for us. We have to find our strength back again quickly.
"We have the potential in us, but first we have to fight.
"It is the same as against Norwich, they were bottom as well and we did not find solutions against a defensive side.
"We have to learn quickly from what happened there and against Schalke. If we do not find these solutions, it is going to be difficult both in the Premier League and the Champions League as well."