Schalke coach Jens Keller is under increasing pressure after the 2-1 defeat at Hoffenheim, with the club saying a crisis meeting would take place on Tuesday.
Seven days ago, Keller appeared to be on firmer ground after taking seven points from three Bundesliga games, including a 2-1 home derby win against Borussia Dortmund.
But his future is again under the microscope after the Hoffenheim defeat and a 1-1 draw with Maribor in the Champions League last Wednesday.
Schalke have eight points from seven Bundesliga games, and face a battle to qualify from their Champions League group, in which they are competing against Chelsea, Maribor and Sporting Lisbon, after two draws -- including a 1-1 at Stamford Bridge.
"The workload [with the Champions League] and also the injuries cannot serve as an excuse, but it's not about looking for alibis," Schalke sporting executive Horst Heldt was quoted as saying by kicker.
"We all wanted Champions League football, and then you have to accustom yourself to the workload.
"We did not lose against Hoffenheim because they were the better team. And we did not draw with Maribor because the opponent asked too much of us -- instead it happened because we did not act like you have to act against those teams."
#INSERT type:image caption:Questions are being asked about Jens Keller's Schalke future. END#
During a football talk show on Sky, a surprised Keller was confronted by one pundit with things he claimed had been said at a team meeting on Sunday, and the coach replied: "Unlike the one or other players from my team, I don't discuss those things in public."
That came after Netherlands striker Klaas-Jan Huntelaar said Schalke needed to put their focus on tactical problems, adding: "The most important thing is to practice those things which are not OK.
"We conceded stupid goals, too easy. And that did not happen for the first time. We talk about it, but you can see that we don't manage to play with stability. And those are things you can coach."
On Sunday, Schalke chief Clemens Tonnies announced a crisis meeting, explaining: "We will analyse what is wrong and make the necessary decisions. We need to get the football machine rolling."
The local Der Westen newspaper said Schalke were about to lose their patience, and headlined: "Schalke crisis meeting on Tuesday -- it's also about Keller."