Dom McKay has stepped down as chief executive of Celtic due to personal reasons.
McKay joined Celtic from Scottish Rugby in April, initially working alongside then chief executive Peter Lawwell before taking over the post on July 1.
His departure was announced to the stock exchange on Friday.
"I'd like to thank the board and everyone at Celtic for their support and wish everyone at Celtic every success for the future," said McKay, who held discussions with Ange Postecoglou before the Australian was appointed as the club's new manager.
Celtic chairman Ian Bankier added: "We thank Dom for his efforts on behalf of the club and everyone wishes Dom and his family very well for the future".
Celtic's director of legal and football affairs Michael Nicholson, who has been with the club since 2013, has been appointed to the board of Celtic plc as acting chief executive officer.
Bankier said: "It has been my pleasure to work closely with Michael for more than eight years now.
"Having been at the heart of the senior executive and reporting to the board, he has a solid grip on how to achieve our immediate and future objectives.
"Michael is an absolute team player and he will lead an experienced and talented team of executives and colleagues at Celtic."