Millwall terminated manager Mark McGhee's contract following the 1-0 home defeat to Preston last night.
Lions fans jeered the Scot and chanted for him to quit after a poor performance.
The club currently lie in eighth position, just one point off the play-off zone.
McGhee kept his players in the dressing room for 30 minutes after the match and they held their own meeting when he had left.
But the former Reading, Leicester and Wolves manager then attended a meeting with chairman Theo Paphitis at which it was decided he leave, along with recently-appointed assistant Archie Knox.
Paphitis said: "We met with Mark. . .and he agreed that it is in the best interests of both parties that there is a parting of the ways.
"The meeting was very amicable. He took over in September 2000 with the brief to get the club into the First Division that season which he duly achieved.
"We then enjoyed a very successful first season at this level, reaching the play-offs the following year.
"Last season was a frustrating one for the club, and whilst expectations were high at the start of the current campaign we have struggled to live up to them.
McGhee won the Second Division championship in his first season in charge of Millwall, and reached the First Division play-offs the following season.
Millwall will make an announcement later today with regard to a caretaker manager, and will invite applications for a permanent manager shortly.