IAN Holloway says he will "deal with" Ricardo Fuller after the striker gestured to Millwall fans during Saturday's defeat at Blackpool.
Fuller was booed after missing a chance and appeared to respond by sticking up two fingers at the away end.
That prompted a further backlash from the travelling supporters and when the Jamaican was substituted, he reacted again.
And Holloway said: "I don't know what he said or what he did but I've spoken to him about it and so have the Millwall players who've been here a long time.
"We've got to stick together so Riccy has got to learn that that's unacceptable in any way, shape or form.
"He feels he was trying so hard and obviously he didn't mean to hit the ball over the bar. He couldn't have tried any harder and he's an aggressive person.
"But that isn't what we want because if my players have done something to turn the fans against them, and brought it on themselves, then I can't stand for that.
"As the manager, I can't really have that and I'll deal with that and deal with him."
Peter Clarke's first-half header from a set piece handed Blackpool victory on a boggy surface at Bloomfield Road.
"The events that led to their goal were pretty bizarre," Holloway added.
"My right back won a great header, didn't touch anyone or do anything wrong but the ref gave a free kick.
"We've got to defend that situation better and convert some of the chances that we created in the second half, otherwise that's what happens.
"Blackpool had nothing to lose but we had everything to lose. We've got a cup game in midweek and we've got to bounce back.
"I'm very hurt at the minute. When you get into certain areas you need to see your players stay composed and that didn't happen."