In a statement released by the club, it has been claimed that the 40-year-old felt that a change in management was required if the team are to retain their status as a League One outfit.
"Following the memorable wins against Nottingham Forest and Liverpool, when the squad proved what they were capable of, Paul had hoped these would be the catalyst to improved results in npower League One, but this has proved not to be the case," read the statement.
"He has been disappointed at the level of commitment and performances and feels that a change is needed if the club is to survive in League One.
"In nearly three years, Paul has shown his tremendous potential as a manager and the board of directors would like to express their appreciation for his commitment, both to the club and the fans.
"Everyone at the club wishes Paul and his family all the best for the future."
Dickov has vacated Boundary Park with Oldham 20th in the League One table.