Saying he was suffering from chronic fatigue syndrome, Schalke 04 announced on Thursday that Coach Ralf Rangnick had quit and it was seeking a replacement.
Assistants Seppo Eichkorn and Markus Gisdol will serve as interim coaches.
Rangnick had joined Schalke after a successful stint at Hoffenheim to replace Felix Magath in March, but he said he needed a break from soccer. Rangnick had helped stabilize the situation at Schalke following Magath's controversial tenure.
"After long and careful consideration, I've come to the conclusion that I need a break," Rangnick said on Schalke's club website. "This decision was terribly difficult to make. But my current energy levels are not sufficient to be successful nor enough to advance the team or the club. I've taken this step with my team in mind and I wish them every possible success for the rest of the season," he said.
Schalke general manager Horst Heldt said Rangnick's decision "deserved the highest respect. We believe health should always take precedence over professional goals and challenges."