Union Berlin, currently bottom of the Bundesliga and without a point since the end of August, have parted company with coach Urs Fischer, the club said on Wednesday.
The departure of the Swiss coach, who has been one of the driving forces behind Union's incredible rise to prominence since his arrival in July 2018, was "a joint decision", said the club in a statement.
"For me personally, and probably for all Union Berlin fans, this is a very sad moment," said Union Berlin chairman Dirk Zingler.
"It pains me that we haven't managed to break the negative trend of recent weeks."
Fischer was at the helm when Union were promoted to the Bundesliga for the first time in 2019, taking them into the Europa Conference in 2021 and the Europa League the following year.
Last season, they stunned the rest of the league with a fourth-placed finish that secured a place in this season's Champions League.
In a difficult season, they have struggled in a group containing Real Madrid, Napoli and Sporting Braga and have taken just one point from four games.
The domestic season started positively with three wins in the first two league games and in the round of 32 in the Cup but Union's year has since turned into a nightmare, with a run of 14 games since August 28 without a win in all competitions.
In the Bundesliga they have just six points from 11 games and, with a worse goal difference than Cologne, they now prop up the table.
The club's under-19 coach Marco Grote will take over as interim coach until further notice.