David Sullivan and Karren Brady were questioned by police in connection with allegations of false accounting and conspiracy to defraud. A statement released by Birmingham City FC said the pair had been interviewed by officers as part of a "longstanding appointment" and they had "happily done so". Seven other people are currently on bail as part of the investigation.
Shares in the company had been selling for 35.5p until the suspension announcement, which came half an hour before the start of trading.
Among those previously arrested during the investigation are Portsmouth manager Harry Redknapp, the club's chief executive, Peter Storrie and former chairman Milan Mandaric.
