Tony Mowbray says his side need to be up for the battle against a Millwall side known for their aerial ability.
The Lions are strong at the back with the likes of Jake Cooper a real danger in both boxes, whilst Gary Rowett also has giant frontman Matt Smith in his armoury at the other end of the pitch.
But whilst many will have the Londoners down as a no nonsense outfit, they have technique and craft in their squad too, with Ryan Woods capable of picking the right pass and Jed Wallace the star under Rowett.
Rovers struggled to get to grips with Mahlon Romeo, who played right wing back in the reverse fixture at Ewood Park, and the boss expects Rowett's charges to go with a similar back five system at the Den this afternoon.
“Millwall play with wing backs, they get it out wide early and swing it into your box to their physical players," Mowbray explained to iFollow Rovers when looking ahead to today's contest.
“It’s a tough place to go and control a game, but first and foremost we need to stand up to them and compete.
“If we can get on top, play our football and push them back, finding a way to get through them is a challenge for us.
“Breaking away, with the pace of Wallace, a good footballer, they’re always a threat at the other end.
“They’re a good team who work extremely hard, carry threats and defend with big numbers," he added.
“We’ll have to go there and roll our sleeves up to get the win.
“The pitch, from the games I’ve watched, is in a similar condition to ours."