The Scot, whose 26-year-long reign at Old Trafford established himself as the club’s greatest ever manager, believes that Mourinho was right to appoint his long-standing deputy Rui Faria to the role.
"You have got to have, in your assistant, someone you have trusted all your life," he told BBC Sport.
"When I came to United, I brought Archie Knox because he was a valuable person for me. I trusted him 100%. Jose Mourinho has had his assistant for years and, quite rightly, has stuck by his own man.
"If Jose hadn't had an assistant, I know he would have taken Ryan."
Ferguson, nevertheless, believes that Giggs has the mettle required to make it in management and supports his former charge’s decision to forge a career away from United.
Mourinho and Ferguson greet each other prior to the 2007 Community Shield (Getty) (2007 AFP)
"It is time Ryan stood on his own feet, got out there and accepted the challenge," the 74-year-old retired coach said.
"I talk about his poker face. He has a bit of steel about him,” he added. “It is such a highly intense results industry, you need people who go into it to have a bit of steel about them, a bit of character and personality."
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Having made more appearances for United than any other player, Giggs was touted as a potential successor to Louis van Gaal following the Dutchman’s dismissal in May.
Giggs worked as an assistant to Van Gaal for the last two seasons, having joined United’s backroom team as a coach under David Moyes.
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