In May 2008 the Scottish legend was quoted as saying he would not be managing beyond three years leading to recent questions that he might call it a day at the end of next season.
However, the 68-year-old rubbished reports in April that he would be departing in the summer of 2011 and now it remains anyone's guess when he will eventually step down.
One thing Ferguson has clarified is that he would not emulate Ron Atkinson's example in 1986 when he inherited a team struggling on the pitch and without silverware.
Ferguson insists he would only relinquish his post when The Red Devils are in a 'good, healthy' position.
"If we hit a bad spell, it would not be the right time to go," explained Ferguson.
"I would not want to put the new manager into a situation where he was taking over a bad team. I want to leave United in a good, healthy position."
Ferguson tried to retire once in 2002 only to perform a quick U-turn following the team's dramatic loss of form and well-timed intervention from his wife Cathy.
"In 2002, I made the decision on a whim," he recalled. "The age 60 sounded good, I'd won the European Cup and a lot of people were saying, 'You'll never do that again.'
"There are a lot of silly things that go through your mind - one line was that Manchester United didn't want another Matt Busby situation and all that nonsense, but after I made the decision the performance of the team went downhill and it was a nightmare.
"On New Year's Eve, we went out for dinner and when we came back I fell asleep on the couch. My wife, Cathy, came in with the three boys behind her, she kicked my foot and said, 'You are not retiring'!"