"I think I'm going to be in football 15 years more minimum," Mourinho said when quizzed about his future on Tuesday ahead of United's away Champions League clash with Benfica.
Ferguson ended his glittering managerial career aged 71 after 26 years in charge of United for whom he won 38 major trophies.
Arsenal boss Arsene Wenger, 67, is the current longest serving manager in English football having taken over the north London club in 1996.
Mourinho, however, said emulating those two's longevity with one club is now "impossible".
He has never lasted longer than four years in any job although he distanced himself with reports linking him to French club Paris St Germain.
"I have my contract which ends in June 2019. We are in October 2017 so I don't know what to say," Mourinho said.
"I told people, and it is true, that I am not going to end my career at United. How is it possible in modern football that any manager lasts 15 or 20 years in the same club. (Arsene) Wenger is the last one.
"If my career was ending in three, four or five years then yes, I would end my career at United. Yes it's true I haven't signed a new contract; but I'm also not thinking about leaving."
Mourinho, who won the Champions League with Porto and Inter Milan, says his immediate focus is on the tricky task awaiting his players in Lisbon against a Benfica side who are still without a point after two games in Group A.
United have won both their games but Mourinho says Benfica are in a false position.
"Benfica need to win the four games that are left," he said. "I have been showing my players that to me Benfica are much better than CSKA (Moscow) or Basel.
"My players are aware that sometimes results aren't an indicator of the value of a team, sometimes circumstances impact this."
(Reporting by Martyn Herman, editing by Ed Osmond)
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