NEIL Harris has warned that Birmingham will be a different proposition under Steve Cotterill when Blues visit The Den on Saturday evening.
Birmingham sacked Harry Redknapp in September after a 3-1 defeat at home to Preston left them second from bottom in the Championship.
Lee Carsley took over on a caretaker basis and saw his side defeat Sheffield Wednesday 1-0, but a 6-1 loss against Hull highlighted the extent of their problems.
Cotterill took full charge for the next game and Birmingham tightened up considerably defensively, not allowing league leaders Cardiff a single shot on goal in a 1-0 win.
Millwall will be looking to rebound after two successive league defeats.
"It was obviously a team that wasn't firing before Steve took over," Harris said. "They had a great reaction on Friday night against Cardiff.
"The tempo and energy from them was very impressive.
"They're a really strong, physical and aggressive side. Steve has put his stamp on it straightaway.
"They've got a brilliant bunch of players – they spent in excess of £10million on deadline day. Any club that can do that in this division is a top-six side, if not pushing for top two.
"We know once they get into a groove they are going to be a strong side this year. But we've got to make sure that on the back of two defeats we make it about us. We have to impose ourselves on the game and combat Birmingham's ability and power.
"We want to impose ourselves at The Den in front of the Sky cameras."
Image: Millwall FC