The 20-year-old French midfielder, who joined West Ham from Paris FC in August 2024 on a five-year contract, posted a statement on Instagram in which he described Sullivan's personal generosity toward him at a difficult point in his early career.
"In a period like this, I wanted to send a personal message to David Sullivan. When I went through difficult times at the beginning of my career, he was one of the few people to trust me. He believed in me, supported me with patience and respect, and it meant a lot to me."
Kanté was careful to draw a distinction between personal loyalty and legal judgment.
"I can only talk about the man I knew and the help he gave me at an important moment in my life. I respect the work of justice and I have confidence that the truth will be established by the competent authorities.
"In anticipation of this, I simply wanted to show him my human support and tell him that my thoughts are with him and his family in this particularly difficult time."
Sullivan, 77, resigned as joint chairman and director with immediate effect on Saturday after learning a BBC Panorama programme was due to broadcast historic allegations concerning his personal life, which he categorically denies. He announced through his lawyers that he would sue the BBC for libel and reserve all legal rights against any outlet that republishes what he describes as defamatory claims.
West Ham United confirmed the departure but stated that none of the allegations relate to the club or any of its operations. Interim CEO Karim Virani continues to lead the day-to-day operations.
Kanté has made 14 appearances for West Ham's first team since joining, still building his profile at the club.