Breaking connection between two fbx game object

Hi, I have a fbx file of a soccer player with animations and materials. I have created two game object with it (two soccer attackers), and whenever I change one of them's materials, the other changes also. Ok, now, I want two make another two players (defence players) from that fbx file, that won't be connected to the other two (the attacker), so I made a copy of the fbx file, and created two game objects from it. But, the result is, whenever I change any one of them (attacker or defencers) all of the four players are affected by it. How can I seperate the first two from tha last two? thanks.