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"He's got the discipline, intelligence and football knowledge you need in the biggest games," Ferguson told the Observer. "Discipline is so much more important in the Champions League, and you need a slightly different type of discipline in Europe. Last season, for instance, one of the things that cost us was Rafael da Silva getting sent off in the return leg against Bayern Munich. There were other things but that was the killer for us.
"The boy was only 19 and he got carried away by the occasion. That can happen but there are some players you can normally rely on to keep a cool head and Park Ji-sung is one of them.
"When you pick teams for big games you need a core of discipline and he's one of the players who can give you that. And he's a fantastic professional. He moves and plays and moves again. That's the asset he's got. He doesn't watch what other players are doing with the ball, he gets himself into another position so he can be involved again. That's his value to us; he can be really important."