Barnsley defied expectations to break into the playoff places last season and just fell short of the final, but following the departure of manager Valerien Ismael over the summer, they have had a far more difficult start to the new campaign.
Now under the management of Markus Schopp, the Yorkshire side collected four points from their first two matches, but have since failed to add another victory.
They come into the game having picked up just four points from the last eight games, and have now lost their last two league outings.
After creditable draws with Stoke City and Blackburn Rovers, Schopp’s side fell to a disappointing 1-0 defeat away at newly-promoted Blackpool on Saturday, before losing to Nottingham Forest last time out.
The Tykes led until the hour mark thanks to Cauley Woodrow’s penalty, but the visitors eventually drew level through Philip Zinckernagel, before Brennan Johnson quickly put them ahead and Lewis Grabban added a third late on to compound Barnsley’s misery.
As a result, they were leapfrogged by the Nottingham side and now sit in 21st spot, and the Tykes will be desperate to reverse their fortunes and move away from the drop zone, but they face a tough test against a Millwall side who have not fallen to a defeat in the last six league games.
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After a slow start to the season, collecting two points from the first four league games, Millwall have managed to build a relatively solid run of form, firstly breaking their difficult start with a 2-1 home win over newly-promoted Blackpool.
Gary Rowett’s men then played out four consecutive draws, firstly holding promotion-chasing West Bromwich Albion before taking points from Swansea City, Coventry City and Nottingham Forest, who posed a tough test with a new manager.
The Lions managed to stretch their unbeaten run to six Championship games last time out, while also making a return to winning ways, as they welcomed Bristol City to The Den on Wednesday