Arsene Wenger accepted his Arsenal side must be more ruthless against Barcelona than they were against Hull when the Champions League holders arrive at the Emirates Stadium on Tuesday.
Wenger's team were left frustrated as they were held to a scoreless draw by second-tier side Hull City in the fifth round of the FA Cup ahead of the first leg of their Champions League last 16 tie against the Catalans.
The combination of a fine display by Hull goalkeeper Eldin Jakupovic and Arsenal's failure to make more of the chances that came their way meant the two teams must now face a replay.
"We need to be more efficient in the final third because today we have more than 70 percent possession and we will not get that on Tuesday night (against Barcelona)," said Arsenal manager Wenger.
"So that means we will have to be more efficient because we will not have as much of the ball," added Wenger, whose team are bidding to become the first club since the 19th Century to win the FA Cup three years in a row.
"I was excited about the game today but of course Tuesday is an exciting game," said the 66-year-old Frenchman.
"We started favourites today (Saturday), we won't be on Tuesday night so on Tuesday night we need great solidarity because we need to defend well, we know that, and make the maximum of our possession what we didn't do today."
Wenger made nine changes to his starting line-up, and left Mesut Ozil and Aaron Ramsey out of the matchday squad altogether.
The manager revealed Ozil has been suffering from a cold all week but insisted the Germany international would be fit to face Barcelona.
"I think I played a team that in my opinion had the quality to win the game and the Barcelona game was not in my mind," insisted Wenger.
"I rested Ramsey and Ozil completely because they have played many games from the start of the season and when I can do it, I do it.
"Ozil was a bit sick over the week so I decided to leave him out and Ramsey has played many times. Ozil will be alright. He had a cold. It's nothing major."