Cousillas attended Tuesday's press conference on the eve of the two sides' last-16 second-leg clash at Camp Nou, with boss Manuel Pellegrini not obliged to carry out media duties due to his two-match suspension from European competition.
The Chilean will watch from the stands on Wednesday as part of his punishment for criticising Swedish referee Jonas Eriksson after City's 2-0 first-leg defeat, with the visitors having it all to do after being outclassed by the Catalan giants in February.
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Cousillas knows that City are faced with a tall order to turn the tie around but has no doubt that they are capable of progressing to the quarter-finals, telling reporters: "We have to try and turn this game around and we have the weapons to do that. That is what we will try to do, fight until the end.
"We will try to be the main characters and take our own risks - of course, with the precautions of facing a great team. In order to beat Barcelona, we will have to play a very complete game."
The City No.2 also backed his side to put their FA Cup disappointment behind them as they attempt to qualify for the last eight of Europe's premier club competition for the first time and win another trophy following their Capital One Cup success at Wembley earlier in March.
"We had a big sense of frustration because we wanted to be back at Wembley and win another cup but Wigan surprised us," he said.
"We have turned the page and we have experienced and quality players, which means we are more united than ever and we have forgotten everything in preparation for [Wednesday]."
Martin Demichelis will play no part as a result of his red card against Barca in the first leg, while Cousillas revealed that centre-back Matija Nastasic (knee) and striker Stevan Jovetic (hamstring) have not travelled with the squad.