Siewert was appointed by Huddersfield in January following David Wagner's departure but he failed to keep the club, who were already facing relegation, in the Premier League.
Siewert was sacked soon after Friday night's home defeat to Fulham, which extended the Terriers winless start to four matches this season.
JAN SIEWERT has demanded a reaction from Huddersfield's players amid calls for his head ahead of tonight's game with Fulham.
The Terriers were also bounced from the League Cup by League One side Lincoln City last week.
Siewert was nearly completely unknown to English football followers when he took over at Huddersfield after Wagner left in January.
Fast-forward almost seven months, and Siewert has been fired by Huddersfield after three games without a win in the EFL Championship.
However, the 37-year-old was dismissed after an Ivan Cavaleiro strike sealed a 2-1 defeat at home to fellow relegated side Fulham.
Club chairman Phil Hodgkinson said Siewert had had little impact on the team's performances during his seven months in charge.
Huddersfield sit 20th (of 24 teams) with just a single point from their first three games of the season.
But the second season in the Premier League proved more hard, prompting Town to search for another manager and again looking towards Germany for his replacement. If they bring the right person in, this can still be a good season, we're only three games in.
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