Sir Alex Ferguson claims "player ego and player power" are the biggest problems facing managers today.
The Manchester United boss has not hesitated to act in the past when he feels players have got above themselves - as David Beckham and Roy Keane both discovered to their cost.
Ferguson believes that with the pressure of results always on them, managers must maintain rigid discipline with the players.
Asked in an interview with UEFA's The Technician magazine about the biggest challenges facing coaches, Ferguson said: "There is a player ego that you have to deal with. As a coach the one thing you must have is control. "You can't afford to let players take charge of a training session, there has to be a strong discipline in the training and in general.
"Simple rules must apply such as time-keeping and concentration at training. "More and more we are dealing with player power. I grew into all of that but a young coach must realise that he is walking straight into all of that. "They have to find a way of navigating all of these pressures.
"Another thing of course is the pressure of results. When I came into the game the media demands were less than we have today, and there were no agents or freedom of contract back then.
"Also, if you have a good chairman and board you are lucky, if not then you have to handle that situation as well."