Arsenal captain Cesc Fabregas insists goalkeeper Lukasz Fabianski is a "very good" goalkeeper despite his mistakes against Porto on Wednesday.
Fabianski, 24, was brought into the side in place of the injured Manuel Almunia in Portugal, but he made two major errors in the match to hand Porto a 2-1 lead going into the second leg. Nonetheless, Fabregas says the squad remains behind him.
"He is a very good keeper," he said. "He had his chance and sometimes it doesn't go your way, but we will stand up and support him until the end because he is a good character and I am sure he will be back.
"Lukasz is strong and we have to be there for him. Sometimes when you are young in a big game, these things happen to you."
Fabregas felt Porto's second goal, which came as the result of an indirect free-kick from a backpass, represented "schoolboy" defending and accepts that Arsenal cannot hope to beat top sides if they make such errors.
"Sometimes we make mistakes which, at the top level, you pay for," he said. "It happened against Chelsea and Manchester United, now again in Porto, so I think we have to try to find the solution to these problems because it is costing us many, many things.
"The other top teams do not make these mistakes as often as we do. We can only change it by working and training I guess."
Sol Campbell, meanwhile, believes he was obstructed by the referee as Falcao rolled into the net following the backpass.
"I accidentally touched the ball back to [Fabianski] and he's picked the ball up," Campbell said. "They have gone to take it quickly and [the Porto player] has picked the ball up, but afterwards the referee is in front of me and basically giving them an advantage.
"It's not good. I can't get in front of the ball. He's basically blocked me to get to the ball. It was better than a penalty because there was no goalkeeper in goal. What can I do?"