Brown, who holds a doctorate in history from the University of Edinburgh, said breaking apart the fiscal union between Scotland and the rest of the United Kingdom would leave Holyrood unable to ask Westminster for financial support, The Scotsman reported Tuesday.
"If you break up the fiscal union, if you break up the sharing and pooling of resources across the U.K., then it's clear that you will either have to cut public expenditure massively beyond what is being done at the moment, or you will have to tax the Scottish people more," he said.
The former Labor party leader predicted there would be a "race to the bottom" in an independent Scotland with different rates for pensions and a lower minimum wage.
"When we pool our resources, the benefit is far greater," Brown said.
He made the remarks while delivering the annual Donald Dewar lecture at the Edinburgh International Book Festival.