Southend United have placed manager Phil Brown on gardening leave while the two parties agree a settlement.
Brown, 58, took over in March 2013 and led Southend to promotion from League Two via the play-offs in 2015.
But a club statement said "this season, to date, has been a disappointment", with seven defeats suffered in their past eight League One matches.
Assistant manager Graham Coughlan and football co-ordinator Brian Horton have had their contracts terminated.
The statement added that the club has "identified a principal target and subject to securing his services will be tasked with replacing the management team without delay".
Southend, who have lost 10 of their 14 away games this season, are 18th and two points above the relegation zone.
"Recent performances have been unacceptable and in the board's view the lack of discipline, Nile Ranger a case in point, has only served to compound the position.
"The club's success as we enter a new era is paramount and we shall adopt a zero tolerance in our efforts to achieve this objective."
Ex-Newcastle striker Ranger, 26, had his contract with Southend terminated on 4 January because of "reoccurring disciplinary issues".
BBC Essex's Glenn Speller
"Was it unexpected? No, not if you look at the statistics. There are some chairman that would've disposed of their manager far earlier than Ron Martin has done.
"But it's maybe a surprise they've done it now, given Phil Brown is out of contract in the summer. There was a lot of feeling around the club that the board would wait until the end of the season, for Southend to secure their League One status and then there would be a mutual parting of ways.
"As for who next, I know that chairman Ron Martin is very keen on Danny and Nicky Cowley at Lincoln. And the other one is Chris Powell, a former Southend player who is very popular with the fans."