Matt Porter has resigned from Leyton Orient's board of directors, claiming that club owner Francesco Becchetti requested that he step down.
Porter was chief executive of the O's for eight years until this summer, when Becchetti bought the League One club.
Porter says he was emailed on Monday by his replacement Alessandro Angelieri asking him to resign as a director.
Orient later said Porter was only due to stay during "the transition period between the old and new regimes".
Porter had earlier claimed the reason given to him by Angelieri for the request to resign was that Becchetti "would prefer the board of directors is kept as small as possible".
|Outgoing Leyton Orient director Matt Porter:|
|"I had been happy and willing to continue serving as a director to assist the new staff with their integration and to provide an element of continuity from the previous regime."|
Italian businessman Becchetti took over Orient from Barry Hearn earlier this summer and subsequently appointed Angelieri as chief executive, with Porter remaining as a director.
A statement on the Leyton Orient website said: "The owner and board of directors would to like to sincerely thank Matt Porter for his cooperation and willingness to stay on the board of the club during the transition period between the old and new regimes.
"The agreement was limited to this period which has now terminated. Mr Porter has therefore left the board and we wish him great success in his career."
Porter has also stepped down from the board of the Football League, where he had served as a League One club representative since June.
"During and since the takeover, I had been happy and willing to continue serving as a director to assist the new staff with their integration in to the club and to provide an element of continuity from the previous regime, as agreed with the new owner," Porter said.
"However, to my disappointment, the position has now changed and as requested, I submitted my resignation on Tuesday afternoon, effective immediately."
Leyton Orient lost in the League One play-off final last season but have endured a shaky start to the new campaign.
Last month, O's manager Russell Slade said he was one game away from being sacked but then the 53-year-old agreed to stay in charge following talks with Becchetti.
However, Slade then became a target to become Cardiff City's new manager and he resigned as boss last week after the east London club denied him permission to speak to the Championship side.
Porter said he had "wonderful memories" from his time working at the Matchroom Stadium.
"It was a position I served with dedication and pride from start to finish," he said.
"We left the club in great shape, on and off the pitch and we did our best for it in every way.
"I wish the club, its hard working staff and players and wonderfully loyal fans every success and thank everyone who has supported and helped me over the years."