Erik ten Hag admitted luck was "not on his side" in his final Manchester United press conference as manager on Sunday, 27 October.
It came after United slipped to their fourth Premier League defeat of the season at West Ham.
They now sit in the bottom half of the table, having won one of their last eight games in all competitions.
In a statement, the club thanked Ten Hag for his work and wished him well for the future.
Ruud van Nistelrooy has been named interim head coach as United recruit a permanent head coach.
