Manchester United midfielder Anderson fears the club could enter a period of decline when Sir Alex Ferguson retires.
Ferguson has been in charge of United since 1986 and he is the most decorated manager in English football history.
The United manager has always maintained he will carry on at the club as long as his health allows.
And having won 12 Premier League titles and the Champions League twice, Ferguson remains desperate for more success.
But he cannot go on forever and Anderson fears United will never be the same again when Ferguson finally calls it a day.
"Manchester United is Alex Ferguson. When he leaves, the club will lose 30-40%, so much depends on him," he told the Grande Área television program in Portugal.
"He is a father to all the players, a very respected person and when he retires the football world will really feel his loss.
"He always helped me and I have a great affection for him. He lives for training and always wants to know how his players and their families are."