"It's very important that we don't concede tomorrow," the midfielder told reporters. "It will be a difficult game.
"We played them four times last season and know how good they are on the counterattack.
"We need to be careful when we lose the ball, we will need to get back quickly in defence. We must press them well.
"If we can win by a goal or two it would be great but keeping them from scoring will be crucial.
"If we stop their best players from scoring I think that we can achieve a good result.
"They have a lot of injuries to important players but we can't think for a second that it will be easy."
The 28-year-old also dismissed claims that his team-mates were tired following two defeats in their last three matches in La Liga.
"I don't think we are tired," the Croatia international added. "We had a bad spell and lost two games. We need to react to that. We need to stay together and maintain our confidence. We have had a great season so far.
"We are fighting for three trophies and aren't giving up in our chase for any of them. Bad times happen in football, that's normal.
"I have to say that we have been playing like a great team, apart from the those two games [defeats by Barcelona and Sevilla]. We are the same team now as before those defeats.
"It's normal that there are moments in the season when you are not [in form]. We are continuing to work to get past those bad games.
"We are focused on tomorrow's match. We haven't lost confidence and tomorrow we'll do our best to win."