Cologne have parted company with coach Peter Stoger by mutual consent after picking up only three points in the Bundesliga this season.
The club, who qualified for the Europa League last season, have drawn three and lost 11 of their league matches, leaving them eight points adrift of second-bottom Werder Bremen.
Stoger was appointed in the summer of 2013 and guided the club back to the top division, leading them to fifth place last season.
In a statement on their official website, Cologne said under-19s boss Stefan Ruthenbeck would take over as coach until the Bundesliga winter break.
The statement said the decision to make a change had come after "an in-depth analysis of the situation," with Stoger having been under contract until 2020.
President Werner Spinner said: "Our responsibility is to try everything in order to stay in the league.
"Until recently, we hoped that we could do this with Peter, his staff, and this team. Despite a positive result against Schalke [a 2-2 draw on Saturday], we unfortunately no longer have this conviction.
"This is why, in the current situation, it is important to bring a stimulus into the position of head coach, despite this being a very difficult and heavy decision for us to make."
Managing Director Alexander Wehrle said Stoger "has written an unprecedented success story" as Cologne's longest-serving head coach but added: "Both Peter Stoger and us have felt in recent days that our joint path was coming to an end, regardless of the result against Schalke."
Stoger said: "It was clear to us on Friday that the Schalke match would be our last. We decided to wait until Sunday to communicate this in order to fully concentrate on the match.
"It is in the best interest of the club, and especially the team, that a decision was made and clarity restored."
The club thanked Stoger and his assistant Manfred Schmid "for their success and loyalty over the years" and said they "wish nothing but the best for the future."