The FA's independent regulatory commission will decide West Ham's punishment on Friday after finding the club guilty of two charges: failure to ensure their supporters refrained from violent, threatening, obscene and provocative behaviour, and failure to ensure their supporters did not enter the field of play.
Related ArticlesFernandes favourite to take over West HamWest Ham eye end of Icelandic liftWest Ham set for takeoverWest Ham ownership saga set for conclusionWest Ham Transfer TalkDerby County 1 Millwall 1 (Derby win 5-3 on pens)West Ham face a range of possible sanctions including being forced to play games behind closed doors and a heavy fine.
The violent clashes led to 64 arrests and the stabbing of a Millwall fan outside Upton Park, and there were pitch invasions during the match.
The FA said in a statement: "An independent regulatory commission last week heard charges issued as a result of the serious crowd disturbances in and around the West Ham United versus Millwall fixture at Upton Park on 25 August 2009.
"It was alleged that both clubs failed to ensure that their supporters conducted themselves in an orderly fashion.
"The independent regulatory commission, chaired by an independent QC, found West Ham United to be in breach of FA rules in the following respects: failure to ensure their supporters refrained from violent, threatening, obscene and provocative behaviour; failure to ensure their supporters did not enter the field of play.
"The commission will reconvene this Friday (15 January) to consider the issue of sanctions.
"The commission found all charges against Millwall not proven.
"The FA will now await the full written reasons from the independent commission before making any further comment."