The Lions are in danger of dropping into the bottom three following successive defeats to fellow strugglers, whilst the Foxes are looking to seal the league title within the next month.
Match preview
Following 10 points from his first four matches back in charge of Millwall after replacing Joe Edwards in late February, Neil Harris has now witnessed his side collect just a single point in the most-recent quartet of fixtures, leaving them in grave danger of dropping down to League One.
If the defeat to bottom side Rotherham United was unacceptable, then Saturday's loss at Huddersfield Town was more on the heartbreaking end of the scale, with Terriers striker Rhys Healey netting a 94th-minute winner for the hosts after coming off the bench in the closing stages.
A glaring issue for the Lions this season has been their inability to consistently find the back of the net in the Championship - Millwall have scored just 38 goals in 41 matches, with only League One-bound Rotherham (32) and 23rd-placed Sheffield Wednesday (33) scoring on fewer occasions.
Having failed to win four-straight home matches prior to the sacking of Edwards in February, Harris has made The Den a relative fortress for Millwall once again, with Tuesday's hosts earning seven points in three home games since 46-year-old's arrival, only being held by promotion-chasing West Bromwich Albion.
Despite their lack of experience in a second-tier relegation battle, the Lions will be leaning on the likes of Japhet Tanganga and Michael Obafemi - who are on loan from Tottenham Hotspur and Burnley respectively - to provide moments of quality at either end of the pitch.
For the first time since the middle of February, Leicester have now recorded back-to-back wins in the Championship to give their automatic-promotion ambitions a major boost, beating relegation candidates Birmingham at the King Power Stadium, although it was not straightforward for the title chasers.
Kiernan Dewsbury-Hall's 12th of the second-tier campaign fired the Foxes into the lead before some casual play from goalkeeper Mads Hermansen allowed Blues' Jay Stansfield to block the Dane's pass, ricocheting the ball into the net, but Enzo Maresca's side secured three points when Stephy Mavididi popped up with a header in the final five minutes.
Saturday represented the first time this season that both Leeds United and Ipswich Town lost whilst Leicester earned maximum points, with Tuesday's hosts sitting pretty at the top of the Championship standings, two points ahead of Daniel Farke's side in third despite playing a game fewer.
Providing a cautious cause for Millwall optimism on Tuesday night, Maresca's men are enduring a three-game winless run on the road across all competitions, including a 1-0 defeat at Ashton Gate versus Bristol City on Good Friday, when the Foxes were well below-par and allowed Anis Mehmeti to net a second-half winner.
Leicester have already visited The Den during 2024 and will be looking for back-to-back successes at the home of Millwall, with a second-string Foxes side coming out on top of a five-goal thriller in the third round of the FA Cup in January thanks to strikes from Cesare Casadei, Ricardo Pereira and Tom Cannon.
Millwall Championship form:
D
W
L
D
L
L
Leicester City Championship form:
L
W
D
L
W
W
Leicester City form (all competitions):
W
D
L
L
W
W
Team News
Millwall remain without the services of striking duo Kevin Nisbet and Tom Bradshaw, meaning that Obafemi and Zian Flemming are set to provide the attacking threat for the hosts on Tuesday night.
Although Harris is hopeful of having Bradshaw and Nisbet back for the final moments of the term, the involvement of Joe Bryan during the rest of the term is in doubt after a leg injury.
The Lions are set to make a few alterations from the XI which lost in the closing moments at Huddersfield, with the likes of Brooke Norton-Cuffy and Casper de Norre banging on the manager's door for spots in the side.
After struggling to deal with the runs of Birmingham's Koji Miyoshi on the weekend, youngster Callum Doyle was subbed at half time, and it is expected that James Justin will go from the off at left-back in this one.
There could be a change at the focal point of the Foxes' attack, with veteran Jamie Vardy surely relishing a midweek game versus Millwall at The Den, possibly replacing Patson Daka in the XI.
Yunus Akgun provided the game-winning assist for Mavididi's headed effort on Saturday, but it is hard to see the Turkey international uprooting either Dewsbury-Hall, Wilfred Ndidi or Abdul Fatawu from the starting side.
Millwall possible starting lineup:
Sarkic; Leonard, Tanganga, Cooper, McNamara; Longman, De Norre, Saville, Honeyman; Flemming, Obafemi
Leicester City possible starting lineup:
Hermansen; Pereira, Vestergaard, Faes, Justin; Winks, Dewsbury-Hall, Ndidi; Mavididi, Fatawu, Vardy
We say: Millwall 1-3 Leicester City
After some vital home victories, a solid away performance at The Den would be a massive statement in the Championship promotion race for Leicester.