Peterborough United manager Darren Ferguson has left the club after Saturday's 3-0 defeat by MK Dons left them 15th in League One.
The Posh have won just one of their last five matches in the league.
In a statement on Peterborough's website, chairman Darragh MacAnthony described Ferguson as "one of the finest managers in our club's history".
"He feels that a new challenge is needed for both himself and the football club," he added.
Ferguson, 43, was in his second spell as Peterborough manager after returning to the club in January 2011.
He led them to promotion to the Championship via the play-offs that season, but they were relegated on the final day of the 2013 season.
"I'm personally very disappointed in our current league position, the performances from our playing squad and the fact we have dropped way below our own standards we set out at as a football club," MacAnthony said.
"Some fans have questioned my own commitment, interest, investment and passion for this football club recently.
"I am hungrier than ever to get this club back into the Championship and beyond and to deliver on the promises I have made to the city of Peterborough."
During his first spell as Peterborough boss between 2007 and 2009, Ferguson - the son of ex-Manchester United boss Sir Alex - guided them to successive promotions from League Two to the Championship.
Coaches Gary Breen, Gavin Strachan and Jimmy Walker, video analyst Stewart England and sport scientist Marc Lindsey have also left the club, with academy manager Dave Robertson put in caretaker charge.