Sir Alex Ferguson believes players today are not sufficiently prepared to become managers.
Opportunities for British coaches to follow in the footsteps of the country's most successful manager appear to be dwindling.
But Ferguson thinks players must start planning earlier for their career off the field, although he acknowledged owners have become more demanding.
He told ESPN FC: "Today I think a lot of players don't make their mind up that they want to stay in the game until it's too late. In other words, they don't have a rounded preparation like I did.
"They maybe take their badges at 32, 33 and then they expect to be managers two or three years later.
"It's a serious result industry. You have to win games. And if you don't have the proper preparation like I did, and a lot of coaches did, you're going to suffer.
"It's a very, very difficult industry. And of course the other side, as opposed to when I started, was that you have different owners.
"They have owners from all over the world, with different ambitions - there's a lack of patience in that respect. But you really need to be prepared to stay in the game. That's the most important message I could give them all."
Ferguson, who won the Champions League twice with Manchester United, also believes there should be no sense of panic at English clubs' struggles in the competition.
For the second year in a row only one English team has reached the quarter-finals, while in 2013-14 no English sides made the last eight.
Spanish teams have won the trophy for the last three years, with Real Madrid twice beating city rivals Atletico in the final.
Ferguson said: "I think success is cyclical. If you think about the '90s, it was AC Milan. In the '70s, Ajax; and Bayern Munich in the '80s; Liverpool, in the '90s; Italy, AC Milan; then England had a great spell with three teams about six years ago all in the semi-final. We (United) were in three finals in four years.
"(Now) the domain is in Spain. There's no question about that. The same question could be asked about the German teams, why are Bayern Munich not winning the Champions League? Why are the Italians not winning it? Why are the French not winning it?
"But that will change, that can change. (Cristiano) Ronaldo will get older, (Lionel) Messi will get older. Can they replace these players?"
Source: PA
