West Ham's stars are set to face an atmosphere unlike anything they've experienced before.
The Hammers travel to the home of their ferocious rivals Millwall on Saturday in what is the first meeting between the two clubs since February 2012.
Given it has been well over a decade since the two clubs last met, the Den promises to be a powder keg waiting for a spark, even if kick-off is scheduled for 12:30pm.
The match has, unsurprisingly, been circled several times over in the calendar of all connected to Millwall, including captain Jake Cooper.
As one of the Lions' longest-serving players, Cooper knows all too well about what Saturday's fixture means to the club.
It's why he predicted the Millwall supporters to generate an ambience like never before the fixture gets underway.
Jake Cooper's verdict on Millwall v West Ham atmosphere
"Since it was confirmed that they would be relegated last season, I think every supporter looked towards this fixture coming up," Cooper said on talkSPORT Breakfast.
"It's great we get them at The Den first, and I'm sure our fanbase will be very excited."
Cooper added: "It will be interesting to see what it's like at their new stadium, how close their fans can impact the game.
"But certainly, at The Den, I think our fans will be incredible. It'll feel like 40,000 in there instead of 20,000. It will be some atmosphere, for sure."
How is the Met Police preparing for Saturday's game?
Given the ferocity between these two teams, the Metropolitan Police have beefed up their operations across the capital.
talkSPORT understands 400 officers will be deployed for the event, underlying the magnitude of the situation.
In a post on X, the Met also confirmed a Section 35 dispersal order will be in place from Bermondsey to as far south as Ladywell, permitting officers to remove anyone causing disorder.
How have West Ham and Millwall performed this season?
West Ham go into Saturday's fixture as the favourites, given they are top of the Championship.
After taking two points from a possible nine in their opening three league fixtures, Nuno Espirito Santo's side have reeled off four wins on the trot.
In that run, the Hammers have scored 16 goals and conceded five, sending a serious warning to rival defences across the Championship.
As for Millwall, they began the season brightly with two wins from as many games.
However, the Lions have gone on to win just once in their last five league games.
But, as the old adage goes in football, form goes out the window when it comes to a derby.
And that famous saying will certainly ring true once the game kicks off on Saturday.