Notts County boss Steve Cotterill is to leave the club when his contract ends on 30 May after failing to commit his future to the League Two champions.
Cotterill, who joined the Magpies in February, said the decision to go was "one of the hardest of my career".
The 45-year-old is now being linked to managerless Portsmouth, having turned down an offer from Coventry.
Magpies chairman Ray Trew said he would begin the search for a replacement "with a heavy heart".
He added: "The job that Steve did for us here will live long in the memory of all Notts County fans and, as is a mark of all great managers, he leaves the club in a much better position than when he arrived.
"To his credit, Steve is a very ambitious manager and he feels that the time is right to take stock of his current situation before deciding upon his next career move, which I completely understand.
"Steve leaves Meadow Lane with my thanks and appreciation and in the hope that he may one day return to the club to manage us at the very highest level."
Cotterill joined County on a short-term contract in February and in April his side clinched promotion to League One.
He stated: "It has been a real pleasure working with such a fantastic group of people from the chairman and chief executive, players, the backroom staff, office workers and ground staff.
"The fans have been magnificent to me and I would like to thank everyone connected with the club for how they have received me since I've been here and wish them all the very best in the future
Pompey administrator Andrew Andronikou told BBC Radio Nottingham on Tuesday that Cotterill is one of eight or nine managers being considered for the vacant position at Fratton Park following the resignation of Avram Grant last week.
And Andronikou told the Nottingham Post: "His CV precedes him. He is the sort of motivator that our players need to take them forward.
"The fact he is out of contract at the end of the month is not a factor. We are looking for the right individual, not at their availability."
Goalkeeper David James, who has been offered a new contract by Portsmouth, has expressed a desire to take over as boss of the south-coast club.
Andronikou hinted that the England player was too inexperienced for the role but did say the 39-year-old would have an input into any final decision.
Cotterill started his managerial career in 1995, succeeding Lawrie Sanchez at Irish side Sligo before taking charge at Cheltenham two years later.
After five years at Whaddon Road he left for Stoke City but quickly left to become the assistant to Howard Wilkinson at Sunderland.
A three-year spell at Burnley then followed before Cotterill took charge at Meadow Lane.
His departure marks the latest twist in what has been a tumultuous season for the Magpies.
The club has been taken over twice, with former England manager Sven-Goran Eriksson arriving as director of football and Sol Campbell signing as a free agent - although both men have now left Meadow Lane.
Cotterill is the third manager to part company with County in the past eight months, alongside Ian McParland and Hans Backe.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.