The Portuguese Football Federation have targeted Queiroz as a replacement for Luiz Felipe Scolari following the Brazilian's move to Chelsea, reports The Daily Telegraph.
Ferguson was determined to keep Queiroz, 55, at United but it is likely he will be searching for a successor once the Portuguese Football Federation has agreed a compensation package.
Happier times: Sir Alex Ferguson alongside Portugal-bound Carlos Queiroz.
"It's not just a question of me wanting to come back," said Queiroz.
"I'm a Portuguese citizen and like every Portuguese I would be thrilled to come back to the national team. But it's not for me to say anything.
'There are two big institutions like the Portuguese Football Federation and Manchester United that are trying to reach an agreement."
Queiroz led the Portuguese youth team to World Youth Cup wins in 1989 and 1991.
He then led the senior Portugal side for three years between 1991 and 1994.
Queiroz also had stints in charge of the United Arab Emirates and South Africa.
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