Sullivan, who owns the Sports Newspapers magazine company renowned for its lewd content, has a controlling shareholding in the club of almost 78 percent.
In a statement to the London stock exchange, a Sports Newspapers spokesman commented: "Sport Newspapers Limited intends to seek interest from
potential purchasers for its entire shareholding in the company...representing 77.96 percent of the issued share capital."
Birmingham City has endured a turbulent time since the departure of long-serving manager Trevor Francis earlier this month. The club's share price on Wednesday was quoted at 27 pence, making Sullivan's stake around £21.6million ($30.8m/B34.58m).
