Giggs ended a 29-year stay at United after new boss Jose Mourinho decided not to retain him on his staff.
Ferguson told BBC Sport: "It is time Ryan stood on his own feet, got out there and accepted the challenge."
"I talk about his poker face," said the Old Trafford legend, who stepped down as manager in 2013. "He has a bit of steel about him.
"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."
"You have got to have, in your assistant, someone you have trusted all your life," said Ferguson.
"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."
Giggs left United after failing to reach an agreement with the club over an alternative role.
Ferguson feels the Welshman has the attributes to deal with the demands faced by the modern manager.
"I think he is ready to manage and he has a lot of quality," said Ferguson.
"He doesn't want to spoil that quality by going to a club where it is sacking a manager every two minutes."