There are concerns that aid agencies will no longer be able to operate in the region if the withdrawal takes place.
It was not immediately clear how long any withdrawal, which for practical reasons would also end the force's presence in the neighbouring CAR, would take.
"There is a [Chadian] political imperative for a withdrawal. It doesn't matter how long it takes, it will be a withdrawal," one diplomat following the situation closely told the Reuters news agency.
"The UN can't operate in a country that doesn't want them. But it also means a withdrawal from CAR."
Chad said earlier this month that it had written to the UN asking it not to renew the mandate, which expires on March 15.
Some diplomats had interpreted this as an effort by Chad to secure a weaker mandate for the force.
"There is no question of that [changing the mandate]," said another diplomat, who also asked not to be named.
"The Chadians are demanding a calendar for the retreat. It will not be long."
The UN, which took over the peacekeeping role from the European Union last year, is mandated to have about 5,000 soldiers in the country.
|The UN took over the peacekeeping role from the European Union last year [AFP]
However, the force is still deploying and there are just over 3,000 personnel in the country.
The UN team currently in N'djamena, the country's capital, is discussing with the authorities whether the withdrawal of troops will be immediate or gradual.
Estimates for a withdrawal range from three months to as long as a year.
An estimated 200,000 refugees from Sudan's Darfur region are in eastern Chad, where they have faced attacks and rape by fighters, according to human rights groups.
Civilians in CAR's north have also been caught up in simmering local rebellions, as well as the broader regional conflict, in which analysts say Chad and Sudan have used each other's fighters in a proxy war.