Peter Lawwell is standing down as Celtic chairman at the end of December, citing "abuse and threats from some sources".
The Scottish champions' board have been the subject of fan protests this season following a disappointing summer transfer window, their exit from the Champions League and with the current side sitting behind Heart of Midlothian in the Scottish Premiership.
New manager Wilfried Nancy has also lost his first three games in charge after succeeding Brendan Rodgers, who resigned in October.