Arsenal boss Mikel Arteta admits they struggled to control the game after their Champions League defeat at Porto.
An injury-time winner from Galeno sees Porto take control of the tie 1-0 after this first-leg.
Arteta said: "We have to manage much better. We cannot win with the way we handled the ball on three occasions in deep areas. If you want to be in the quarter-finals you have to beat your opponent and this is what we will have to do at the Emirates now.
"We lacked threat. We lacked aggression, especially with the ball in the final third. We can do better.
"I think they're a team that's very well-organised defensively and they break your rhythm all the time. There are certain things we will have to do much better, we know what to expect."
He added: "We couldn't even touch anybody because everything was a free kick. We will learn from that, prepare better, and go and do it."