After bringing 10 Premier League titles and two European Cups to Old Trafford during an incredible 22-year reign, Ferguson need have no concern about losing his job.

At 66, the Manchester United boss has earned the right to end his tenure at a time of his choosing.

He realises many of his management rivals are not so lucky. Roy Keane has just quit as Sunderland boss, while another of Ferguson's former players, Paul Ince, is now under severe pressure at Blackburn.

And with Howard Wilkinson, Alan Curbishley and Sam Allardyce, the favourite to replace Keane, out of work, Ferguson accepts job security is virtually non-existent.

"It is a very precarious industry," said Ferguson.

"Very few managers last more than three or four years with a club nowadays and the lifespan of a manager is getting shorter and shorter.

"I count myself fortunate to spend so long at one club.

"I have not had to go through that turmoil. It is horrible."

Ferguson acknowledges the demands placed on managers are greater than they have ever been.

The vast amounts of TV money on offer to the top flight plays a major part as clubs desperately try to preserve their status.

But he also feels the attitude of supporters has changed markedly too.

"Crowd participation has become more volatile," he said.

"The other day I saw of photograph of a United game against Leeds. All these warriors like Stiles, Hunter, Charlton and Crerand were scrapping in the middle of the pitch. But when you look at the crowd there is not a bit of emotion. They are just watching the spectacle.

"You would not get that now. The fans would be screaming blue murder. It is a very emotional industry. That emotion can get to everyone. You lose three or four games and you are in trouble."

The precise reasons behind Roy Keane's departure from Sunderland are not known.

However, it is difficult to escape the feeling Keane was increasingly uncomfortable with his position at the Stadium of Light.

Although chairman Niall Quinn spent three days trying to talk his fellow Irishman round, Keane's exit means there will be no reunion with Ferguson when Sunderland tackles United at Old Trafford on Saturday.