Ferguson: Beware financial collapse in football
"There is an awful lot of expenditure and you say to yourself, 'Where is it going to end?'," Ferguson was quoted as saying in Saturday's Guardian newspaper.
"This is exactly what was happening in the business world two years ago. There were warning signs and everyone knew there were, yet they carried on because it was so easy to access loans.
"In the football world the warning signs are there but nobody seems to be bothering about it. You wonder where it's going to end and what is going to happen if one major club were to... collapse," added Ferguson.
The Scot seemed to have in mind clubs like Real Madrid and Manchester City, who spent huge sums on players in the transfer window with the Spanish side paying a world record 80 million pounds for United winger Cristiano Ronaldo.
Ferguson said vast expenditure does not always equal automatic success.
"It is not easy winning things, definitely not easy, and they will soon find out," he said.
United, second in the Premier League two points behind Chelsea, play Bolton Wanderers at Old Trafford on Saturday.