Linton Brown has left his post as Barnsley's chief executive.
The 48-year-old took over from Ben Mansford and was put onto the board in June after two spells as head of commercial.
The Reds statement read: "Yesterday, Linton Brown, chief executive, left the Club. This is a very critical period of the season for Barnsley Football Club given the dynamics of the transfer window.
"The Club has now commenced its search for a replacement. In the meantime, Chairman Maurice Watkins, supported by external advisors, will continue to assist Paul Heckingbottom with recruitment in particular."
