The 44-year-old coach has been out of work since leaving Inter Milan last summer.
He has been linked with a number of high-profile clubs, including Chelsea - but his agent Giorgio De Giorgis claims an offer to join United was snubbed earlier this season.
"Where will he go? He would want to go abroad," said De Giorgis.
"A little while ago there was contact with United but they were offering him only the role of Ferguson's assistant. And that didn't suit him.
"I really believe that next year he will return to coaching a big club.
"I think that everyone aspires to have someone like him, he has showed on the pitch how well he knows how to make his teams play and that he knows how to win."
Mike Phelan is United's current assistant manager, having replaced Carlos Queiroz when he became Portugal coach in September.