Ferguson does praise the former England captain's tenacity and longevity, but wonders whether Beckham might live to regret swapping European football for Major League Soccer and the Los Angeles Galaxy in 2007.
"At some point in his life, he may feel the urge to say: I made a mistake."
Ferguson on Suarez/Evra affair:
One of the great controversies of Ferguson's latter years at United is the racism row which erupted between Patrice Evra and Luis Suarez, of the club's great rivals Liverpool.
Suarez was hit with an eight-game ban in December 2011 for racially abusing Evra, with Ferguson highly critical of how then Liverpool manager Kenny Dalglish handled the affair.
Suarez's refused to shake Evra's hand ahead of a match later on in the 2011-12 season, an act which drew Ferguson's ire.
"A club of Liverpool's stature should have done something about that, but he played in the game all the same," recalls Ferguson.
"I called Suarez a 'disgrace to Liverpool' and said they would be wise to 'get rid' of him."
Ferguson on England job:
The passionate Scotsman reveals he was twice offered the chance to manage the England national team, in 1999 and 2001. But it was not a job he entertained accepting for one minute.
"There was no way I could contemplate taking the England job," he says. "Can you imagine me doing that? A Scotsman?
"I always joked that I would take the position and relegate them: make them the 150th rated country in the world, with Scotland 149."
Ferguson on Cristiano Ronaldo:
He is in no doubt that Cristiano was "the most gifted player I managed."
"He surpassed all the other great ones (players) I coached at United. And I had many," says Ferguson of the Portuguese star.
Ronaldo joined Real Madrid for a then world record fee of £80 million pounds in 2009, a transfer which Ferguson describes as "a clever move by them."
"It was a way for Florentino Perez, their president, to say to the world 'We are Real Madrid, we are the biggest of the lot.'"
It marked the end of a two-year pursuit of Ronaldo by Real Madrid.
Perez's predecessor as Real president Ramon Calderon made a bid to sign the explosive forward in 2008 which irked Ferguson, with the Scot telling Ronaldo "I'd rather shoot you than sell you to that guy now."
A year later, Ronaldo was unveiled in the Spanish capital.
Ferguson on Barcelona:
In 2009 and 2011, Ferguson saw his United team lose to Barcelona in European Champions League finals.
Barcelona's style of play was unrivaled in Ferguson's eyes and he describes the Catalan team as "the best team ever to line up against my Manchester United sides."
Ferguson reserves special praise for Lionel Messi, the four-time FIFA Ballon d'Or winner who was become Barcelona's talisman.
"The group of world-beaters who formed around Messi were formidable," declares Ferguson. "I felt no envy towards those great sides. Regrets yes, when we lost to them, but jealousy, no."