Sir Alex Ferguson says controlling the dressing room was key to his success with Manchester United.
Ferguson's revelations were made during a lecture at Harvard Business School, which has just been published.
"There are occasions when you have to ask yourself whether certain players are affecting the dressing room atmosphere, the performance of the team, and your control of the players and staff," he said.
"If they are, you have to cut the cord.
"There is absolutely no other way.
"It doesn't matter if the person is the best player in the world.
"Some English clubs have changed managers so many times that it creates power for the players in the dressing room. That is very dangerous."
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