City boss Guardiola said: “Gabriel has to be himself, we need his goals and that's why we won the last game.
“If he puts this idea in his head he can do it every game.
“Not just with him but for all the players, confidence has to be there in the heads, not because of good or bad performances, winning or losing games.
“There are some things that are undeniable, the mentality and how strong they are. We have to learn with all athletes, we'll not bei in the high level and playing if he didn't have quality.
“They can control it, they don't need the manager to speak to them, they have to believe they are good enough and show how good they are.
“All the time it's there, if they score goals the confidence rises, likes if a keeper doesn't' concede goals the confidence rises.
“Normally here we speak about what happened in the past, the recent past - but everything has changed, couldn't care less.
“It's about tomorrow at 5.30 and the players decide who is going to win.
“United have huge history and their quality is always there but we must try to beat them. I speak to my players to see how to beat them."