Moyes took over from his fellow Scot following the retirement of Ferguson — British football’s most successful manager — after the end of the 2012/13 season.
Some pundits said former Everton manager Moyes’s already difficult task had been made harder by a lack of succession planning on the part of his illustrious predecessor.
But Ferguson said Moyes, who was sacked less than a season into his time at Old Trafford after United failed to qualify for the lucrative European Champions League, had made a mistake in not retaining former assistant manager Mike Phelan in his backroom staff.
“It is an insult to say that I left an ageing squad,” said Ferguson during an interview with actor and United fan James Nesbitt at London’s Drury Lane Theatre on Sunday to publicise his updated autobiography.
“Chelsea have seven players over 30 but nobody talks about them being an old team.
“It is easy to defend myself against all of that because all the statistics are there.
“I think he should have kept Mike Phelan, he was a United man; loyal, hard-working and a good judge of the players.
“My advice to David was that he should maybe keep Mike Phelan.
“I was always supportive of David, whenever he called I gave him the advice I would have wanted when I was manager.
“But David will do well in the future: life doesn’t end when you leave United.”
Meanwhile Ferguson reiterated his support for new United manager Louis van Gaal, who on Sunday oversaw the club’s creditable 1-1 draw with Premier League leaders Chelsea at Old Trafford.
“He has that philosophy, stubbornness and determination to succeed, I’ve got every faith he will be a success,” said Ferguson of the veteran Dutch boss.
“I have absolute faith that he’s the right man for the job.”
Ferguson added van Gaal, whose team are currently eighth in the table — 10 points behind Chelsea — had been hampered by a succession of injuries, particularly in defence.
“It’s been one step forward and two steps backward for them so far this season, in terms of injuries,” Ferguson said.
“(Radamel) Falcao looks a player and (Angel) di Maria will do well,” he added of two of van Gaal’s high-profile signings.
“Once he (Van Gaal) can get people fit and a settled, regular back-four, then that’s the first route to progress.”