City assistant manager Cousillas attended Tuesday's press conference on the eve of the second leg of the sides' last 16 clash at Camp Nou, with boss Manuel Pellegrini not obliged to carry out media duties due to his two-match UEFA suspension.
Pellegrini will watch from the stands on Wednesday as a result of his punishment for criticising Swedish referee Jonas Eriksson after City's 2-0 defeat in the first leg at the Etihad Stadium, so Argentine Cousillas and Brian Kidd will take on greater responsibility.
City have it all to do after being outclassed by the Catalan giants last month and head into the game on the back of a shock 2-1 FA Cup quarter-final defeat against Championship side Wigan Athletic on Sunday.
Barca have problems of their own, though, as they were beaten 1-0 at struggling Real Valladolid on Saturday and are now third in La Liga - four points behind leaders Real Madrid.
Cousillas knows that City are faced with a tall order to turn the tie around, but the 56-year-old has no doubt that the Premier League side are capable of progressing to the quarter-finals.
He said: "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 number two also backed the Premier League 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 League Cup success at Wembley earlier this month.
"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 tomorrow."
Martin Demichelis will play no part as a result of his red card against Barca in the first leg.
Cousillas revealed that centre-back Matija Nastasic (knee) and striker Stevan Jovetic (hamstring) have not travelled with the squad.
