McCarthy, a coach on Erik ten Hag’s staff for two years, left in the summer and was replaced by Ruud van Nistelrooy.
The South African believes a few United players may have faked injuries to avoid tough games.
“Times have changed, generations have changed,” McCarthy told SuperSport.
“Back then, the coach would slap you hard. “Benni I need you, wake up”. I didn’t take it personally because maybe he was right.
“If you shout at a player now, he has a mental breakdown. It’s more delicate. There are lot of things now that you can’t do or say. You have to think of the mental aspect and how it will affect them. Is a player okay with his life and his family?
“That’s the reason he (Jose) never succeeded. I think he was too honest and too direct for players to accept that he only wanted the best because he knows your full potential. That’s what you have to do to be a world-beater.
“We accepted it because we knew. 'Hey, this guy is going places and let me do what he wants because I’m going with him'. At United, they were (saying) 'where am I going to go with him? I’m already at United. Boss, I’m injured. I don’t want to play because I don’t want to get criticised'.”