A 3-1 loss at home to third-placed Middlesbrough on Wednesday saw the Blades' lead in the race for automatic promotion cut to seven points, while their hosts dropped out of the top six following a defeat to Coventry City on Tuesday but remain a single point outside of the playoff places.
Match preview
Millwall have enjoyed another positive campaign thus far in their bid to earn promotion to the Premier League, and after a 3-0 beating of Rotherham United on New Year's Day, they sat in a strong position in the playoff places with 39 points on the board from 25 Championship outings.
They have been unable to cement a position in the top six since, though, having only added two more wins and seven more points to their tally in the last five matches, after also losing 2-0 at The Den in their last meeting with Sheffield United in the FA Cup third round - making that the second two-goal defeat to the Blades this term.
That exit from the competition was followed by a 1-0 loss away at Middlesbrough, but they bounced back with a one-goal triumph away at Cardiff City, before making it three games unbeaten with a draw against Sunderland and a 2-1 victory over Queens Park Rangers at Loftus Road last Saturday thanks to goals from Duncan Watmore and Oliver Burke.
Aiming to extend their run to four league games without a defeat, the Lions made the trip to take on Coventry City on Tuesday, but they left empty-handed after being unable to find a response following Viktor Gyokeres's 67th-minute opener.
Although that defeat saw the London outfit drop out of the playoff places, they do remain just a single point behind sixth-placed Watford and two worse off than fifth-placed Sunderland, with the chance to quickly reclaim a top-six spot if they can make a return to winning ways on Saturday.
That will be no easy task, though, as Sheffield United arrive hoping to bounce back from a rare defeat and get back on track in their automatic promotion bid.
An eye-catching run of form after the World Cup break late last year saw the Blades establish themselves in the top two in England's second tier, as they went 10 games unbeaten in the Championship with eight of those being wins, while also advancing to the fifth round of the FA Cup with the victory over Millwall and an eventual triumph against fifth-tier Wrexham after a replay at Bramall Lane.
Following that progression, which booked them a round-of-16 tie with Tottenham Hotspur, Paul Heckingbottom's side comfortably beat Swansea City 3-0 at Bramall Lane on Saturday, with Sander Berge, Jack Robinson and Oli McBurnie getting on the scoresheet, to maintain their 10-point lead over Middlesbrough, while also having a game in hand ahead of their meeting with the third-placed side on Wednesday.
The South Yorkshire had the perfect start in that top-of-the-table clash, as McBurnie headed in an opener inside five minutes, but Chuba Akpom drew their visitors level later in the first half before Cameron Archer hit a brace after the interval to seal a crucial away victory and cut the gap to seven points.
Even despite that outcome, Heckingbottom's men do remain in a strong position with a healthy lead and a game in hand, provided they are able to quickly return to the form they have displayed in recent months, and without their boss on the sidelines after his red card in the Boro defeat, they will be desperate to immediately bounce back to winning ways at The Den to take another step closer to a top-two finish.
Millwall Championship form:
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Sheffield United Championship form:
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Sheffield United form (all competitions):
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Team News
Millwall's attack should again be led by Tom Bradshaw, who has seven league goals to his name so far this season, while Zian Flemming will offer plenty of additional threat having hit the net 10 times in England's second tier since arriving from Fortuna Sittard.
Oliver Burke and Duncan Watmore are also vying to start in the attacking line, with the former hoping to feature against his former club, while both got on the scoresheet away at QPR after their recent arrivals at The Den.
Elsewhere, Jake Cooper should again be joined by Leeds United loanee Charlie Cresswell in the middle of a back four while Billy Mitchell will continue to play alongside George Saville in the engine room.
Even after Tuesday's disappointing display, Sheffield United will likely come into Saturday's game with an unchanged starting XI, with defenders George Baldock, Enda Stevens and Rhys Norrington-Davies remaining sidelined by injuries alongside midfielder Tommy Doyle and strikers Billy Sharp and Rhian Brewster.
Given those absences, talismanic forward Iliman Ndiaye, who has contributed 10 goals and seven assists in the Championship so far this season, will again be joined up front by Oli McBurnie, who has scored in back-to-back league games to take his tally to 11 for the season in 23 second-tier appearances.
Sander Berge and Manchester City loanee James McAtee will again join Oliver Norwood in midfield with Jayden Bogle and Max Lowe continuing to play in wing-back roles.
Millwall possible starting lineup:
Long; McNamara, Cresswell, Cooper, Wallace; Saville, Mitchell; Burke, Flemming, Watmore; Bradshaw
Sheffield United possible starting lineup:
Foderingham; Ahmedhodzic, Egan, Robinson; Bogle, Berge, Norwood, McAtee, Lowe; Ndiaye, McBurnie