The Ukrainian was last in the ring in August when he retained his WBA, IBF and WBO belts after a split-decision victory over Anthony Joshua in Jeddah.
Talks over an undisputed heavyweight contest with WBC-belt holder Fury took place immediately after Usyk's success in Saudi Arabia, but the Briton will instead take on Derek Chisora at Tottenham Hotspur Stadium next month.
It means the wait for all the titles to be on the line continues and, while Usyk is determined to fight Fury, his religious beliefs means they must get in the ring by March 4 or be prepared to wait until later in the year.
"Right now my team is seeking conversations with Tyson Fury and he is really an unpredictable person so we can't guarantee when," Usyk said.
"For me, the idea would be to fight maybe early February or beginning of March, like March 4, because I am an orthodox Christian.
"During the great fasting before Easter I do not fight, so it should be all before or then after orthodox Easter (April 16).
"I want to fight with Fury because I need the fourth belt and I don't want to fight with anyone else until I have the fourth belt."
Usyk was in Lisbon to speak alongside Parimatch Tech chief executive Maksym Liashko about the ongoing war in his country and the importance of highlighting the actions of Russia.
The 35-year-old insisted Ukrainian people would continue to "fight back against the aggressor and bully" but raised the possibility of fighting for the world heavyweight titles in Kyiv.
He added: "The organisers are trying to figure out where they can earn more money.
"For me, yes I would really like to fight in Ukraine and Ukraine is really capable of hosting this kind of fight. I would be really happy to see it happen in the Olympic Arena in Ukraine. But it is not me who chooses the venue so I guess it will (this time) be Saudi Arabia."
Before Usyk can turn his attention to an eventual meeting with Fury, he will watch on with interest on December 3 when his rival does battle with veteran heavyweight Chisora.
It will be the third meeting between the British pair and the ex-cruiserweight questioned why it needed to take place.
"I don't know why he needs this fight," Usyk said.
"Maybe he thinks because it would be one year without a fight, now he needs it. I think it is some manoeuvre because I don't know why he needs this."