"Duty to inform" is probably a bit OTT as this guy is probably retained, if at all(!), in some sort of consultancy capacity. I doubt he's a fully paid up employee with official accountabilities.
Having said that, if a shareholder asks the question of the board as to whether there is a person employed as a strategic go-between of the head coach and the chairman I think they ought to furnish that shareholder with an honest and frank answer, particularly if the individual in question is alleged or perceived to have had "hands-on" influence in the day to day football strategy.