Arsenal drew a blank with Hull City at the weekend.
The Gunners head in to the clash coming off the back of a 0-0 draw with Hull City in the fifth round of the FA Cup.
The North London club had numerous opportunities to defeat Hull, yet wastefulness in front of goal meant they could not find a way past the Championship side despite having 23 efforts on goal.
Mertesacker pointed out how his side cannot afford to be so wasteful against Barcelona, saying: “Overall, we missed a bit of something and we have to come back quickly in three days time.”
“We have a very important game, the first leg against Barcelona, and we will see the fans again, it will be another buzzing night but it is up to us how we perform.”
"It is down to us, we produced a good defensive performance [vs Hull] but overall in the final third, that little final pass at the end, we always rushed ourselves at times to finish so we need to learn from that.”
Arsenal know that chances against Barcelona this week may be somewhat limited, therefore the likes of Theo Walcott, Alexis Sanchez and Olivier Giroud must make the most of what comes their way.
The Catalans head into the clash boasting a Spanish record 32 games unbeaten in all competitions, having not lost an encounter since a 2-1 defeat against Sevilla last September.
Luis Enrique’s men top La Liga, are in to the Copa Del Rey final and are looking to become the first team in recent history to win back-to-back Champions League titles since its official reform.