With United slumped in the bottom half of the Premier League table and David Moyes under increasing pressure, it had been suggested that Ferguson might eventually be ushered out of retirement in order to salvage the situation.
However, speaking to US TV network PBS, Ferguson ruled that scenario out, and underlined his belief Moyes is the right man for the job.
"I'm not interested in managing again or getting myself worked up about Manchester United's results," said the 71-year-old.
"You would be throwing your money down the drain if you put any money on me coming back as a manager.
"United are in good hands with David Moyes. He will be fine. He's a good manager.
"I made my decision. The timing was perfect. There is no way back for me now. I've got a new life.
"I want to go to the Kentucky Derby and the US Masters, the Melbourne Cup. I want to visit vineyards in Tuscany and France."
In a wide-ranging hour-long interview, Ferguson, who left United in the summer after almost 27 years in charge, revealed he was asked to manage Chelsea not long after Russian Roman Abramovich bought the club.
"They used an agent to approach me when Abramovich first took over the club," he said. "And I said, 'No chance'.
Source: PA
Source: PA