David Sullivan has resigned from his position as joint-chair of West Ham.
The 77-year-old, who has been on the board at West Ham for over 16 years, has stepped down ahead of "impending publication of serious historic allegations".
A club statement released on Saturday read: "West Ham United can confirm that joint-chair David Sullivan has stepped down from his position with immediate effect.
"Mr Sullivan has also resigned as a director of both WH Holding Limited and West Ham United Football Club, having been made aware of the impending publication of serious historic allegations.
"It is understood none of the allegations relate to West Ham United or any of its operations.
"Through his own legal representatives Mr Sullivan denies any illegal conduct and has taken the decision to step down in order to avoid disruption to the club while he addresses the matter privately."
The statement also confirmed that interim CEO Karim Virani will continue to be responsible for leading the club's day-to-day operations and will report into the remaining board of directors.