A number of spectators entered the field after Neil Harris' 71st-minute winner for Millwall against Leeds and the FA have confirmed that they are to make enquiries and gather information from all concerned parties following the clash.
Leeds goalkeeper Casper Ankergren was subjected to taunts by the Millwall fans following the goal and also had missiles thrown at him, and Scotland Yard have confirmed that one man has been arrested on suspicion of assault.
"There was something thrown at me, I didn't see what it was as I turned my back on it," Ankergren told BBC Sport. "It's very bad for football and Millwall should be punished. I was pushed in the back by one of the fans that came on the pitch too. It
should never happen, fans should not be allowed on to the pitch.
"I'm not sure what the security were doing as no-one came to remove them. They are meant to be here to protect the players, it's not good enough. I hope something will be done. It is a disgrace to football."
Millwall have confirmed that any fans arrested will be banned from all their games for the foreseeable future and that Ankergren has received apologies from the club.