After visiting the recently liberated city last week, Fr Emanuel Youkhana of the Assyrian Church of the East told Catholic News Service: "I don't see a future for Christians in Mosul."
Islamic State seized control of power in Mosul in August 2014, forcing Christians to either convert, pay a tax or die, causing thousands to flee for their lives.
The Iraqi army began an offensive to gain back control of Mosul in October 2016.
After months of fighting, Iraqi officials raised the national flag over the eastern part of the city on 27 January.
Shiite fighters patrol a neighbourhood recently liberated from IS on 25 January
Iraq's special forces troops hold an IS flag during a parade to celebrate the fully liberation of the eastern side of Mosul on 27 January
Fr Youkhana - who runs Christian Aid Program Northern Iraq - joined the military convoy to assess the situation in the city.
"The churches were used as warehouses by Daesh," he said. "They used the churches to store what they looted from Christian and Yezidi villages, but as the end neared they sold the buildings to local contractors, who started tearing down the walls to reuse the steel inside.
"If the army hadn't entered for another couple of weeks, the buildings might have been completely destroyed."
The priest reported that there was extensive damage to churches and the former homes of Christians.
"Christians aren't going to come back to stay. The churches I saw were not destroyed with bombs, but by the everyday business operations of the community. How can Christians return to that environment?
"It's unfortunate, because Mosul needs their skills. Most Christians were part of the intellectual and professional class here, they were doctors and lawyers and engineers and university professors. But I don't see how they can return," he said.
Meanwhile, Archbishop Bashar Warda of Erbil has unveiled his plans to support Iraq's displaced Christians.
He said that once Mosul was declared safe and cleared of booby traps left by IS fighters, he hoped that Iraqi Christians would be able to return to "the homes of their forefathers". He told Aid to the Church in Need that at least 50 per cent of displaced Christians want to return home.
Aid to the Church in Need will help to provide funds to support the rebuilding of villages around Mosul.
The charity has supported urgent housing, food and pastoral care projects with more than £13.7 million since 2014.
Christians once made up a sizable minority in Iraq. ISIS is believed to have killed over thousands of Christians in the last two years, displacing and imprisoning many more.