Traianos Dellas has resigned as coach of AEK Athens, the Super League club announced on Tuesday.
The 39-year-old former Greece defender, a key member of his country's unexpected triumph at Euro 2004, had guided AEK to two successive promotions to regain its top flight status.
Bankruptcy in 2013 had forced the team out of the Super League for the first time in the club's history.
"AEK would like to announce that the coach Traianos Dellas has submitted his resignation and it has been accepted," said a club statement.
"Mr Dellas will coach the players for the final time tomorrow. The management of AEK thanks him for his contribution to the team for the past two-and-a-half years and for his part in helping the club return to the Super League."
AEK's under-20 coach Stelios Manolas will take up the post on an interim basis until a new coach is found.
Although AEK was thumped 4-0 by leaders Olympiakos Piraeus last Saturday, Dellas' decision still comes as a surprise after AEK has begun the season in promising fashion. The Yellows are fourth in the standings with 13 points from seven matches, eight points behind Olympiakos.
Spaniard Manolo Jimenez, who coached the club to success in the Greek Cup in the 2010-11 season, is the front runner among potential candidates to replace Dellas, local media reported.