Central Coast coach Paul Okon has quit the A-League club with immediate effect.
The off-contract former Socceroo is understood to have walked away on Tuesday afternoon after failing to come to agreement with management on a number of issues.
Okon's two-year contract was due to expire at the end of the season.
"Both Paul Okon and the Central Coast Mariners have been in discussions for several weeks about the strategic direction of the football club," the Mariners said in a statement.
"Given the club's future strategies and plans, both parties have agreed that it is best to end the association immediately to give the club an opportunity during this vital period to re-sign players and target new players."
The Mariners also confirmed assistant coach Ivan Jolic would also leave immediately, with youth mentor Wayne O'Sullivan appointed as caretaker for the remainder of the season.
Okon wished the club the best for the future.
"I will forever be grateful to the Mariners for the opportunity they gave me," Okon said.
"I thank the players for their commitment and the fans for their support."
His decision follows another disappointing campaign for the Mariners, who had started promisingly and even reached the top four but have long since slipped to ninth place after an 11-game winless run.
As an expert on youth development, Okon was signed from the Young Socceroos on the eve of last season with a mandate to get the best out of a young playing group at a cash-strapped club.
In 2016-17, the 45-year-old did his best with a squad largely recruited by sacked predecessor Tony Walmsley, but was able to bring in his own team this season.
But a lack of depth, particularly in the front third, has yielded an equal league-low 25 goals. The Mariners sit just three points in front of cellar dwellers Wellington with four rounds remaining.