The Blues were humbled 3-0 at home by Bayern Munich in the first leg of the round of 16 tie.
Now they must go to Munich and win by three clear goals to have any shot of progression.
But Giroud is not giving up entirely.
"It's going to be almost impossible," Giroud said at Stamford Bridge to reporters.
"We need to go there with belief, to believe that we can score. You never know. They scored three here, so we need to go there and score three and not concede. I'm not joking.
"So, we have nothing to lose, we're going to play our game maybe with more freedom. They are a team with a lot of experience. When I was on the pitch I was thinking 'everything is so smooth'.
"They have played together for a very long time, they have a very good understanding with each other. They played well and you have to recognise this. But you don't have to keep your head down and we've got to bounce back as soon as possible.
"They were the better team so it's very deflating obviously. We need to move on and focus on what's next now, even if in the first half we could have done better because we had opportunities to score.
"But when you concede two goals in four minutes it's very hard to come back psychologically, to turn the game. They played a very good game, and they are a very good team."