Guto Llewelyn, journalist for ITV Wales and Swansea supporter, has his say on The Swans...
The Welsh side were Play-Off finalists last campaign, but have struggled to replicate their fine form this season.
"The club has gone through massive changes since the Play-Off Final last year. We have a new manager, a totally new style of play and a very different squad, so it's been a transitional season with a lot of ups and downs as we start from scratch.
"I think fans knew we would struggle to repeat the success of recent seasons but there's a lot of support for what the manager is trying to do and hopefully we can build on the foundations we've set this season."
Last time out, Swansea humiliated rivals Cardiff City 4-0.
"I'll be honest, I'm not sure we as fans are ready for another game so soon after the derby, which was one of the all-time great away days. To go away to your biggest rivals and hammer them 4-0 is the stuff dreams are made of. It was so incredibly satisfying and the players clearly loved it every bit as much as we did.
"Hopefully it will give us confidence, but after the wild celebrations on Saturday, I think a lot of us are still hungover so who knows what we'll be like at The Den."
Russell Martin joined the club in the summer and has implemented a possession based style of play.
"We have by far the best possession and passing stats in the division, which tells you everything you need to know about our style of play.
"The difficulty at times has been transferring that possession into chances and goals. When it clicks, it's stunning to watch but when we don't click, we can look very slow and stale on the ball and scarily open when the opposition attack. Only the top two have scored more goals than Swansea from open play, so there are definite positive signs."
Top goalscorer Joel Piroe has dropped deeper to accomodate the inform Michael Obafemi, who scored a brace at the weekend.
"Piroe has settled brilliantly since signing in the summer, although he's now playing in a slightly deeper role to make room for Michael Obafemi who's found his scoring touch since Christmas. They, along with Jamie Paterson, form a dangerous front three who are scarily clinical.
"The other class act in our side is Flynn Downes. Signed from Ipswich in the summer, he's like a Championship version of Declan Rice, a brilliant footballer in midfield who loves a tackle and alongside the excellent Matt Grimes, he usually dominates midfield."
Llewelyn expects a much more open game in comparison to September's 0-0 draw at The Swansea.com Stadium.
"Millwall are obviously in brilliant form and still have a chance of making the Play-Offs. In order to make the top six, you probably need to win home games against teams like The Swans so unlike back in September, when Millwall were very defensive, I expect them to be more open and ambitious this time around, which should make for a more exciting game.
"If we play the way we did against Cardiff, we'll have a good chance of getting a result but I also think there's a good chance of an "after the lord mayor's show" type of performance, which would play into Millwall's hands."