The club's sporting director, Horst Heldt, said that "there have been situations that we've not been so happy with."
Schalke during the winter break is going to review its staff after a "turbulent" half-season, according to club sporting director Horst Heldt.
Although the Gelsenkirchen outfit has reached the last 16 of the Champions League, inconsistent domestic form means it is seventh heading into the Bundesliga break. Heldt said a review of Schalke's entire operation will now be undertaken.
"Overall, it's been a turbulent half a year," Heldt told Sky. "It's important that we draw our conclusions and realise what we've done well and what we've done badly. That means the work of every individual is examined, including the coaching team. We do this every six months as a rule. There have been situations that we've not been so happy with."
The latest setback for Schalke came in a 0-0 stalemate at Nuremberg on Saturday, a match coach Jens Keller missed through illness.