Beware Subprime Mark II: Asset Manager

There are still major concerns about Europe's economy and sovereign default is still a possibility, but the U.S. may be heading into even stronger headwinds with the rollover of loans having the potential to become "subprime mark two," according to Yogi Dewan, founder of Hassium Asset Management in London.

European banking stocks surged at the open Thursdayfollowing the release of the methodology that will be used for the stress testing of 91 euro-zone banks.

Some of the gains were driven by the jump in US stocks in Wednesday's session, but sentiment was also helped by the fact that stress tests will not force banks to test what would happen if a euro-zone member defaulted.

Dewan said there is some relief that the tests would not be tougherbut warned investors to be cautious when looking at the sector in both Europe and the US.

“We remain very cautious," Dewan told CNBC. "In Europe there remain big risks associated with a possible sovereign default and a slowdown in growth."

But there even more things to worry about in the US market, he added.

Subprime Mark II

“American banks are facing a potential 'subprime mark two' with the resetting of the mortgage market over the next 18 months," Dewan said. "There a $1 trillion of commercial loans to be rolled over and another $750 billion of residential mortgages and I don’t think the market is paying attention to this threat yet."

Dewan also sees the chance of major writedowns on credit cards and personal loansand believes the recent slowdown in US growth will continue.

Goldman Sachs' strategy team disagrees, saying in a report that a "slow 1-2 percent GDP expansion (in the US) would be sufficient to generate positive earnings growth from current level."

Get Out Of Japan

With the Chinese economy showing signs of slowing significantly, Dewan is also worried about Japan.

“GDP to government debt stands at around 180 percent, which is twice the level of most developed countries," he said. "Deflation is still a risk and the yen is strong. With China also slowing we cannot rule out a downgrade of Japanese sovereign debt."