Bayer Leverkusen coach Roger Schmidt is under increasing pressure following three consecutive league defeats.
Leverkusen began their Bundesliga campaign with narrow victories over Hoffenheim and Hannover, but have been without a goal since Hakan Calhanoglu's 18th-minute strike at Hannover.
A pair of 3-0 defeats at Bayern Munich and Borussia Dortmund, sandwiched a 1-0 loss at home to Darmstadt, have seen them drop from third to 13th.
And speaking ahead of the home match against Mainz on Wednesday, sporting executive Rudi Voller told Express: "Some players have fallen into a deep sleep.
"The players have to awaken from their slumber as soon as possible, hopefully against Mainz."
Schmidt started with five attacking players, including former United star Javier "Chicharito" Hernandez, against Dortmund -- but saw his side outplayed and fail to muster much threat.
In defence, left-back Wendell had a bad day and was berated by attacker Karim Bellaribi when he conceded a penalty.
Voller said: "That defeat was a wake-up call. Our style of play is based on unity, and that hasn't been the case recently."
While he did not blame Schmidt, German newspaper Bild named the 48-year-old as one of the reasons for Bayer's downfall.
The paper hit out at fitness coach Oliver Bartlett, with German football magazine kicker also questioning whether Leverkusen players were lacking in fitness.