Arsenal manager, Mikel Arteta, believes his team is not ruthless enough.
The Gunners had to settle for a 1-1 draw away from home against Benfica in the first leg of their round of 32 Europa League tie.
Now they will have to get a win or a 0-0 draw at home to progress into the last 16 of the competition.
Arteta told BT Sport: “We were very dominant and created some big chances. We have to be more ruthless.
“It was disappointing the way we conceded the goal. We gave them the ball then it was 1-1 and all to play for.
“We conceded a corner then from the corner we did not react quick enough and conceded the penalty. Looking at it it’s difficult to judge. We had a great reaction and scored a great goal.
“We tried to maintain the level. Both teams dropped in the last 20 minutes. But overall we should leave the ground with more.”