Dom McKay has resigned as CEO of Celtic for personal reasons.
McKay joined Celtic from Scottish Rugby in April, he initially worked alongside then CEO Peter Lawwell, before taking office 1. July.
His departure was announced to the stock exchange on Friday.
"I would like to thank the board and everyone at Celtic for their support and wish everyone at Celtic every success for the future,McKay said, who held discussions with Ange Postecoglou before appointing the Australian 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 the very best for the future".
Celtic's Director of Legal and Football Affairs Michael Nicholson, who has been in the club since 2013, has been appointed to the board of Celtic plc as Acting Chief Executive.
The banker said: "It has been a pleasure to work closely with Michael for over eight years.
“As he was at the center of senior management and reported to the board of directors, he has solid knowledge about it, how to achieve our immediate and future goals.
"Michael is an absolute team player and will lead an experienced and talented team of executives and colleagues at Celtic."