Queiroz, 54, is frustrated with his Old Trafford assistant role and is looking at other options.
He is in his second spell as Alex Ferguson's No 2 after an unsuccessful term at Spain's Real Madrid.
Queiroz said: "I need to reflect on what I want to do in this last part of my career.
"In December I'm going to stop and think about myself.
"My contract is perpetual and caters for various options. But I only have one life and one career. I am going to think about it and go for the route that makes me most happy."
Fergie has said he would like Queiroz to succeed him, but he is clearly not prepared to wait.
He said: "I read Sir Alex said that one day he would like me to be United's main coach. That is one reason I am in this project but I'm not desperate about it.
"In your personal and professional life you always have more ambitions."
One option would be a return home. He said: "To coach in Portugal is a possibility."