NEIL Harris is wary that Brentford are "capable of springing into life at any stage" ahead of the Lions' derby in west London on Saturday.
Brentford were second after seven games of the season but have not won a league game since then and Millwall would climb above their rivals with a victory at Griffin Park.
The Bees have suffered three defeats in their three games under Thomas Frank, who took over as manager after Dean Smith departed for Aston Villa.
"Thomas was instrumental in what was going on under Dean Smith anyway, as assistant manager and coach," Harris said. "Not a lot is going to change, personnel is not going to change.
"There will be slight alterations in style of play, defensively and attacking-wise, but not huge amounts.
"Brentford are still a very clever football team with very good individuals, some very impressive younger players that are going to go beyond this division in the near future.
"So we know it's going to be a tough game. We know they've not been on a great run of form, but that they are capable of springing into life at any stage.
"When Brentford have their moments in the game, which they will do, then we need to be at our best."
Jed Wallace is a doubt for Millwall with a calf strain, but striker Tom Elliott has recovered from a dead leg that forced him off in the 3-0 win over Ipswich last Saturday.
Brentford will be without midfielder Kamo Mokotjo after he went off in last weekend's 1-0 defeat at Norwich.
Frank knows what threats Millwall carry. He said: "We know it is a long season so it is about being calm, doing what we believe in and continuing to improve in training.
"We want to improve small bits in the way we play and it is good to have had a full week to work on that.
"Millwall are a very hard-working, honest and efficient team that we respect a lot.
"We know they can make life difficult for every single team in this league. There will be spells when we need to defend well and we have to be aware at set-pieces."
Possible Millwall team:
4-4-2: Amos; Romeo, Hutchinson, Cooper, M Wallace; Skalak, Leonard, Williams, Ferguson; Elliott, Gregory.
Brentford 5/6 Draw 13/5 Millwall 3/1
Brentford 1-0 Millwall (Sawyers 47'; Gregory missed pen 80'); Millwall 1-0 Brentford (Saville 1').
Image: Millwall FC