Monic Houde, who chaired the firm’s human resources and corporate governance committee, said “strictly important personal reasons” were behind her resignation.

François Duffar, a co-founder and former vice chairman of Cossette has made a bid to gain control of the company, which provides strategic planning and research services through its agencies Nucleus and Impact Research in Canada, Cossette in the US and Miles Calcraft Briginshaw Duffy in the UK.

Last week the board knocked back Duffar’s offer of C$4.95-a-share, dismissing it as “highly opportunistic”. Cossette has engaged its financial advisers to solicit alternative proposals.

Announcing her resignation yesterday, Houde said: “I support without reservation all the decisions made by the board of directors to date in relation to the proposal to acquire Cossette. I have full confidence in the current management team and that the board will fully evaluate all strategic options for Cossette for the benefit of all shareholders.”