Atletico travel to the Camp Nou for the first leg next week currently sitting top of La Liga, one point ahead of Barca with seven games remaining.
"We're second in the league now but we know we're up against a very strong team," he told Barca's official website. "Atletico Madrid are in brilliant form at the moment. Maybe the only handicap we face is that we play the return leg at the Vicente Calderon, but I think the tie is 50-50.
"Perhaps we're slight favourites because of our history. But if we look at how both teams are playing, it's very even. It'll be decided by the details.
"We don't usually enjoy playing them because they don't give you any space. They're good at closing down the areas where we try to create things. In Diego Costa they have a player who's in brilliant form. He makes the most of every situation."
Barcelona were knocked out in the semi-finals of the Champions League by Bayern Munich last season.