The Gunners will start their Europa League campaign against the Bundesliga side on Thursday, and the Spaniard makes it clear that it is a very important competition for the club this season.
"Our focus is on Thursday's game," the Spain international told website IBTimesUK.
"It is a very important match to start the Europa League on the right foot.
"We have to give our best and only after that will we start to think about Chelsea.
"The Europa League is a very important competition for us.
"We know that if we have the possibility of winning it, we will return to the Champions League next year, which is one of our targets.
"It's a competition that we know we can win and we're going to fight as much as in the other competitions to do it.
"Whoever plays, we are going to give our best."