Vladimir Antonov has resigned as chairman of Portsmouth after the club's parent company was placed into administration.
The Russian businessman, whose company Convers Sports Initiatives bought Pompey in June, has also quit as a director of the club following the news.
Portsmouth Football Club Limited continues to trade and is not in administration.
Pompey chief executive David Lampitt said: "After the extraordinary amount of work put in by so many people over the last 18 months to get to this point, it is incredibly disappointing for the club to find itself in this position.
"I want to assure staff and fans that we will continue to do everything possible to safeguard the position of the club and its longer-term future."
An official statement released by Portsmouth said: "The club's parent company, Convers Sports Initiatives plc (CSI), has been placed into administration.
"Vladimir Antonov has resigned as chairman and director of Portsmouth Football Club.
"The club has funding in place for the short term, but will now be seeking alternative investment for its longer-term requirements."