If its serious then it wont be fighting themselves. Living in London its been very easy to get tickets for this game. I would not be surprised if there are those media darlings west ham in there.
Can I also remind Brighton fans of the rioting that Brighton have been involved in at places like Chesterfield, Palace, Brentford, and fighting last season at west ham and those Brighton fans in jail for the fighting against Spurs before a frienly or the leeds fans attacked in Brighton or the southend fans stabbed in our last away game down there. So its not just Millwall. If West ham or some other fans have gone to cause trouble then it will still be millwall who will get the blame.