A tight encounter is expected at London Road between two of the division's struggling sides, who between them have won just two of their last 17 matches, and Ferguson believes Posh will have to bide their time.
"It's a big game tonight for sure," he told the Peterborough Evening Telegraph. "If we win we will be seven points ahead of Milwall with a game in hand and that would be a great position to be in.
"We have a big week with two home games and we know that we need to perform at London Road.
"Millwall are a big strong side and we will have to defend well at set-pieces to get a result. They'll be well-organised like all Championship teams so we will have to patient while trying to break them down."