"The amount of working capital you'd expect the government to take into this would be around $3 trillion to $4 trillion," said Simon Johnson, a senior fellow at the Peterson Institute for International Economics, Fortune reported Tuesday.
Johnson, a former chief economist at the International Monetary Fund, said the first round of bailout funds -- roughly half the $700 billion financial rescue package passed in October -- has left banks without enough of a cushion and that toxic assets are still weighing them down.
Paul Miller at FBR Capital estimated the bailout would cost at least $1 trillion for the nation's eight largest banks alone.
U.S. banks are still struggling. The KBW Bank Index has fallen 35 percent this month after dropping 50 percent in 2008.
"The big banks are a hope trade right now," Johnson said.