The Catalans hold a 1-0 lead from the first leg and have beaten their rivals in each of the last three Clasicos.
"It doesn't mean anything that we have won the last three Clasicos, tomorrow is another footballing war," Xavi told reporters.
"They will be out for revenge, they will come here hurt, they have lost the last three. They will come here wounded, I am sure."
"Madrid come tomorrow and they can beat you perfectly well -- they can against any team," said Xavi.
"They have a lot of experience, they are used to mounting comebacks. They are still favourites for me.
"We were better in the league game and in the Super Cup, but we weren't in the first leg."
Despite Eder Militao's own goal handing Barcelona a narrow victory at the Santiago Bernabeu, Ancelotti's side dominated the Catalans.
Xavi said he expected Los Blancos to try and stop his team controlling the match and playing their usual possession football.
"(I predict) an aggressive Madrid, who want to take the ball off us, pressing us," added Xavi.
"We need to have a lot of personality tomorrow to keep the ball."