Barnsley have parted company with head coach Daniel Stendel following a run of 10 Championship games without a win.
The 45-year-old German took charge at Oakwell in June 2018 and led the Tykes to promotion from League One in his first season in English football.
Adam Murray has been appointed caretaker manager with the club currently second from bottom.
Barnsley have not won since beating Fulham 1-0 at home on the opening day of the season.
Stendel's final game in charge was a 5-1 defeat at Preston North End on Saturday, a game they went into with a back four with an average age of 20.
In his final post-match interview, he described Barnsley as having "played like a youth team".
"The second half was the worst that I can remember at Barnsley," the former Hannover 96 boss told BBC Radio Sheffield.
"You can see the players want to fight and never give up, but we've lost the confidence after 10 games without a win.
"Every player has enough problems of their own during a game and it's difficult when others can't help out.
"At the moment, we're playing like a team that is not good enough for the Championship."
Stendel led Barnsley to an immediate return to the second tier last season following relegation in 2017-18, with the South Yorkshire side finishing second in League One and going through the entire campaign unbeaten at home.
But key members of the promotion-winning squad left Oakwell over the summer, including goalkeeper Adam Davies, centre-backs Liam Lindsay and Ethan Pinnock and striker Kieffer Moore.
A dozen players were brought in, most of them on four-year contracts, but the majority are aged 22 and under.
Stendel won 31 of his 66 games in charge of the club, the third highest win ratio of any permanent manager in the club's history.
Barnsley's next Championship game is at home against Swansea City on 19 October.
Andy Giddings, BBC Radio Sheffield sports editor
Many fans would blame the club's recruitment policy, not the head coach for the circumstances they find themselves in.
And Reds fans are angered that a popular, promotion-winning, manager has left at a relatively early stage of the season.
The use of a fairly brutal statement hasn't gone down well either.
Barnsley use a 'Moneyball' spreadsheet model for finding players. Not all of them are going to work and trying to make the ones that do arrive work in a harder division than League One was always going to be tough.