DANNY Shittu believes Millwall's reputation could be severely damaged by the violent disorder seen during Saturday's FA Cup semi-final defeat to Wigan at Wembley.
The Lions, the Football Association and the Metropolitan Police have launched an investigation after crowd trouble broke out during the second-half at the national stadium.
Police say 12 people from the Millwall end of the ground have been arrested but said a "significant post-match review will take place to identify those responsible for committing offences."
Shittu said: "At this club, you can do five things right and then one thing wrong and it sets things all the way back again. Everyone has to behave. Those days are over now.
"But there is a minority trying to mess up the name of this club and it has got to stop. I am sure the chairman and the club will deal with it.
"This club is a good club, otherwise I wouldn't be standing here speaking to you as the face of it. It's a club that I believe in. There's a lot of good things at this club.
"I am trying to promote that side of things but when this sort of thing happens, it makes it so much harder and everyone will start believing the stereotypes again.
"It's not just the players who are representing Millwall, it is the fans aswell. They need to stop doing stuff like that. You should come to the game and be passionate about the team.
"You don't get anything out of fighting. They have to stop this now. We are trying to put Millwall in a good light and we have been doing that.
"I'm not here just to play the game – I'm here to represent the club. But we can't be doing our part if the supporters aren't doing theirs. The vast majority of our fans were brilliant."