The Lions' slip-up at Huish Park on Good Friday has left Kenny Jackett's men six points adrift of second place Posh with only four games left to play and they know that only a win will do at The Den this evening.
The Millwall boss will be hoping on-loan winger James Henry will be fit to be included in his squad and he must also decide who will lead his forward line for tonight's crunch-clash, which will also be the first televised game at The Den since 2005.
Gary Alexander, Neil Harris and Jason Price will all be vying for one of the two striker berths with youngster Ashley Grimes hopeful for a place on the bench.
Should The Lions win this evening they will be at least guaranteed a play-off spot if Tranmere lose at home to Hereford.