Ferdinand was released by United last month.
Speaking to reporters, the former England captain revealed that - when in the caretaker manager's role at United - Giggs had told him that, should he be offered the job full time, there would be a place for him at the club.
"When Giggsy took the job he had to look at it like he was going to be in the seat for next season and he made it clear to me I would have stayed and been part of his plans," Ferdinand said.
"But things change in football, you have to move on. The dynamic there has changed so you have to dust yourself down and get on with it."
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