Derby County have sacked manager Nigel Clough following the 1-0 defeat by rivals Nottingham Forest.
Clough, 47, had been in charge of the Rams since January 2009 but the loss to Forest left Derby in 14th place in the Championship.
"After much consideration, the board feel it is time to move Derby County forward to the next level," read a club statement.
Saturday's defeat at the City Ground was Derby's third in eight days.
"The search is well under way to identifying and appointing a successor, and further announcements will be made in due course," the statement continued.
"The ownership group remain steadfastly committed to the club and maintain their desire to compete at the top end of the Championship this season."
Clough, who followed in his late father Brian's footsteps when he took over at Derby, is the fourth manager to lose his job this season.
Clough was the fourth longest-serving manager in English football, behind Arsenal's Arsene Wenger, Exeter City's Paul Tisdale and Oxford United's Chris Wilder, and the longest serving in the Championship.
Clough began in management at Burton in 1998 after a successful playing career which included spells at Nottingham Forest, Liverpool and Manchester City.
He also won 14 caps for England and ended his playing career at Burton.
Derby's owners, General Sports and Entertainment, led by chairman Andy Appleby, took charge of the club in January 2008.
At that stage Derby were in the Premier League, although they were relegated that season.