LONDON (MarketWatch) -- Kenneth Rogoff, the former chief economist of the International Monetary Fund, reportedly said Tuesday that a large U.S. bank will collapse in the next few months. "We're not just going to see mid-sized banks go under in the next few months, we're going to see a whopper, we're going to see a big one, one of the big investment banks or big banks," Rogoff told a conference in Singapore, according to a Reuters report.