CHELSEA must stop Barcelona's best-player-in-the-world Lionel Messi in their Champions League semi final - or be punished.

So admits  Salomon Kalou , having faced the Catalans and suffered the backlash before.

“We learn from the past,” said the Ivorian, of their meeting with the side in the 2009 semi.

“That is a good feeling already. We learn from the past games, and we know that if we give them the opportunity and give them the chance to play, they will punish you.

“That is a good thing to know. It is still a difficult game but I believe that we can pull it through.”

Asked about their mercurial forward Messi, Kalou said: “He is the best player in the world. No doubt. You can't have any discussion about that.

“We hope that in two games against us he won't be the best player, that he won't be on his top form.”

Chelsea have found in the past that, if they nullify Barcelona's attacking might, they can themselves find weaknesses in their opponents defence.

“Every team has a weakness in some part,” Kalou added. “ And they have their own weakness. We know that we can play on that. We know they haven't been so confident at at the back, conceding a lot of goals. That is something that we can play on.”  

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