Fortune played alongside striker Rooney for two years at Old Trafford and says no-one will escape the axe if they are not performing because of the club's high standards.
He said: "It's not sad, because it happens to every human being.
"Sometimes these things happen in life. No-one is undroppable.
"You need to perform. From my experience at United, if you don't perform, the boss will drop you and someone else will come in.
"So you always had to keep the standard and that was every day in training, how you applied yourself, how you behaved, your mentality."