Mertesacker is quoted by The Telegraph as saying: "We are not at our best. Football-wise we lack a few things. We have to be honest to ourselves and train harder.
"Everyone knows that it is a difficult start to the season for us and confidence is not how we want it. Again, it is away from home on Saturday and again I think we have to do better with our own possession, to put more pressure on [opponents], not to lose so many balls in the middle of the park, to play more in wide areas.
"I think it is better to expose them there, instead of playing one-twos through the middle. It doesn't work as much as last season, so we have to work on that. The passing game is not as efficient as last year."
Arsenal travel to Sunderland on Saturday.