The pandemic is compounding the forces of conflict and climate change, which were already slowing poverty reduction, the bank said.
By 2021, this could rise to as many as 150 million, it added.
Extreme poverty is defined as living on less than $1.90 (£1.50) a day.
The projected increase would be the first since 1998, when the Asian financial crisis shook the global economy.
Before the pandemic struck, the extreme poverty rate was expected to drop to 7.9% in 2020.
But now it is likely to affect between 9.1% and 9.4% of the world's population this year, according to the bank's biennial Poverty and Shared Prosperity Report.
At the other end of the scale, billionaires have seen their fortunes hit record highs during the pandemic, with top executives from technology and industry earning the most.
The world's richest saw their wealth climb 27.5% to $10.2tn (£7.9tn) from April to July this year, according to a report from Swiss bank UBS.