Birmingham City director Panos Pavlakis has resigned with immediate effect.
A statement on the club's website says he is stepping down in order to "pursue other opportunities" but Sky Sources understand he has become increasingly frustrated at the club's direction.
Pavlakis was brought in three-and-a-half years ago to sort out the financial situation at the club.
Pavlakis was made a director in 2014, and in the absence of any CEO or managing director at the club, ended up running the football operation.
He appointed managers Lee Clark and Gary Rowett, and had a role in the appointment of Gianfranco Zola, but crucially he wasn't involved in the process that saw Harry Redknapp take over for a further year after helping secure City's Championship survival.
Birmingham now have a number of directors associated with the Chinese owners running the club in England, but there is no specific figurehead or CEO.