Meanwhile, fresh off getting the better of Queens Park Rangers on their travels, the home side now only sit four points adrift of safety.
Having gone into lockdown with a three-match unbeaten streak, Millwall boss Gary Rowett would have had every confidence that the run would be extended against Derby County last weekend.
Although an early goal put the Lions on the right track, they were ultimately undone by a stunning treble from teenager Louie Sibley, who subsequently fired his team level on points with Millwall.
With the East Londoners sitting three points adrift of the playoffs, Rowett is now tasked with trying to lift his players ahead of a crucial period of their season.
While the gap to the top six remains relatively small, some of their rivals have began to build momentum, meaning that Millwall can ill-afford a second successive defeat.
Despite their next opponents occupying a place in the bottom three, Barnsley will feel that they should be regarded as the favourites to prevail on Saturday afternoon.
After back-to-back setbacks without scoring a goal against Reading and Cardiff City before the lockdown, Gerhard Struber may have felt differently heading into their game at QPR last weekend.
However, with the narrow success taking Barnsley's recent record to four wins from half-a-dozen outings, they remain as one of the form teams in the division.
The bigger picture shows the Tykes as being at least one victory away from catching struggling Hull City, but they are now only seven points adrift of 17th-placed Wigan Athletic.
With three successive meetings with teams around them coming up shortly, including Wigan, Struber knows that another maximum return at the weekend could put the club in an increasingly favourable position.
Barnsley Championship form: WWWLLW
Millwall Championship form: WLDDWL
Struber will likely have to make at least one change with Elliot Simoes, the scorer of the decisive goal against QPR, struggling with a muscle problem.
After being handed his debut last weekend, it would come as a surprise if Romal Palmer does not continue in the centre of Barnsley's midfield.
Millwall are boosted by the return of Mason Bennett after the Derby County loanee was unable to face his parent club.
Barnsley possible starting lineup:
Sahin-Radlinger; Sollbauer, Andersen, Williams; Ludewig, Palmer, Mowatt, Ritzmaier; Brown; Chaplin, Woodrow
Millwall possible starting lineup:
Bialkowski; Romeo, Pearce, Cooper, M.Wallace; Molumby, Woods; J.Wallace, Bennett, Ferguson; Smith
We say: Barnsley 1-1 Millwall
Both clubs have reached a stage in their season where it could be perceived that only wins will do. However, we are backing the two teams to cancel each other out at Oakwell, aware that defeat will put them significantly further away from their respective targets.