Hamburg fired coach Michael Oenning on Monday after the worst league start in the club's history.
The Bundesliga club said on its website that under-23 coach Rodolfo Cardoso will take over with immediate effect on an interim basis.
''This decision hurts a lot. In the last two days since the 1-0 (home) defeat to Moenchengladbach, and following many intense talks, we came to the conclusion that we had to make that decision,'' Hamburg sporting director Frank Arnesen said.
''We will now pull out all the stops in order to find a successor to Michael Oenning. Rodolfo has our full support.''
Hamburg is last in the Bundesliga with one point from six league games, conceding 17 times. Saturday's loss was the fourth in a row.
Hamburg has never been relegated from the German top flight, and is the only team to have played in the Bundesliga continuously since it was formed in 1963.
''It's also understandable for me that the club wants to go a different way in the current situation,'' said Oenning, the first coach to be fired in the Bundesliga this season.
''He accepted the decision very professionally,'' said Arnesen. ''Of course he's sad, but the club also comes first for him.''
Former coach Huub Stevens is the favorite to replace Oenning on a permanent basis, returning to the club he has saved from relegation before, in 2007.
''The new coach has to have passion, strong tactical ability and be able to pull their weight,'' Arnesen said. ''It's also very important that he speaks German and knows the environment.''
After the 45-year-old Oenning took over from Armin Veh on March 13, Hamburg won only one of his 14 games in charge - the first.
Oenning never played the same formation for consecutive league games this season.
''For us players, it's hard because we don't really know what we need to change,'' Hamburg left back Marcell Jansen said Saturday.
Cardoso's first game in charge will be at sixth-place Stuttgart.
Arnesen had proclaimed his support for Oenning after the latest defeat, saying: ''Michael Oenning will sit beside me on the airplane to Stuttgart and again back to Hamburg. I can make that clear. He's our plan A, B and C.''
At a media conference on Monday, however, the 54-year-old Dane - who has overseen 17 transfers each way since taking over in the summer - said he changed his mind when he asked himself if Hamburg could beat Stuttgart on Friday.
''I felt we had little chance if things carried on as before,'' Arnesen said. ''I didn't just think with my heart but also with reason ... My job is to do what's best for Hamburg.''
The 42-year-old Cardoso, who played for Hamburg from 1996 to 2004, began coaching the club's youth teams in 2005. He also played for German sides Werder Bremen, Freiburg and FC 08 Homburg after transferring from Argentine side Estudiantes in 1989.
Cardoso scored 47 goals in 220 Bundesliga games, and one in eight appearances for Argentina.
Germany great Franz Beckenbauer, who had a two-year spell at Hamburg from 1980 to '82, said he knew ''no coach in the world who can help Hamburg.''
''The new coach would have to be a wizard ... A normal being has no chance in the short term,'' Beckenbauer said.
