Soros said Britain is particularly vulnerable to the global economic downturn, and could have trouble financing its mounting debt, The Times of London reported.
He warned also that next week's G20 summit of world leaders in London was the last chance to avert a British depression.
"You have a problem that the banking system is bigger than the economy ... so for Britain to absorb it alone would really pile up the debt," Soros said.
As for getting help from the IMF, Soros said it was "not a likelihood," the newspaper reported.
The Times noted that Britain has not sought IMF help since 1976, when inflation was approaching 27 percent and the government sought a loan.
Soros said he did not blame British Prime Minister Gordon Brown for failing to prevent the economic crisis.
"He underestimated the severity of the problem but so did most people. Part of the perceived role of a leader is to cheer lead so you can't really blame him for that."