The Premier League leaders face the formidable Neymar and the rest of the star-studded Paris St Germain side in the first leg of their last-four tie at the Parc des Princes on Wednesday.
It is only the second time City have reached this stage of the competition and the first since Guardiola took charge of the team in 2016.
Guardiola conceded defensive work is not his side’s greatest strength, but he expects them to make up for that in other ways.
“We are not good in our defensive departments,” he said. “We are good with the ball. Our strong point defensively is because 11 players run a lot.
“Tomorrow, unfortunately, we will have to run more and more because PSG are so strong.”
Guardiola was relaxed as he spoke for more than half-an-hour at the pre-match press conference and he feels this is the best mindset to adopt.
He said: “Always it happens in my career in this competition, when I arrive in the semi-finals. I was always calmer than in other competitions, other moments.
“I don’t know why but I have the sense of the work well done already, and I see the team so happy and in the right moment, for the tension and the responsibility. In the same moment I say, ‘OK we are going to try to do a good game’.
“I have that feeling, but in this competition, with the quality, you can win or lose. You never know.”