Four Greek banks raised more than $11 billion in sales last year, according to data compiled by Bloomberg. Foreign investors piled in as they bet on a rebound in what Euroxx Securities SA analyst Maria Kanellopoulou called “a vote of confidence for the Greek banking system.”

North American firms including Paulson & Co., BlackRock Inc., Capital Group Inc., Fidelity Management & Research Co. and Fairfax Financial Holdings Ltd. bought stakes in the banks around the time of the deals, separate data show.

Twelve months on, their confidence hasn’t been rewarded. Shares in the lenders that raised capital — Eurobank Ergasias SA, National Bank of Greece SA, Piraeus Bank SA and Alpha Bank AE — have fallen by an average of 56 percent since the sales, the data show. Those losses could rise sharply as the country skirts with the prospect of defaulting.

“If the Greek government defaults, investors will own a huge amount of defaulted exposure on their balance sheets,” said Diego Valiante, a research fellow at the European Capital Markets Institute and the Centre for European Policy Studies.

Even if Greece doesn’t default on its debt payments, some banks may still fail because of soaring non-performing loans and an excessive amount of Greek government bonds, reducing their value further, he said. “Any exit will be a penalizing one,” Valiante said.

Greece has closed its banks until at least July 6 and there will be a daily cash withdrawal limit of 60 euros as the Greek government tries to stop lenders from bleeding more cash. Bank transfers or payments abroad will be banned. Prime Minister Alexis Tsipras has pledged a July 5 referendum on bailout terms previously proposed by creditors.

Top Shareholders

The U.S. funds that took stakes last year are now among the biggest shareholders in the banks, excluding the state-owned Hellenic Financial Stability Fund, a vehicle set up in 2010 to distribute European funds to help recapitalize Greek lenders.

Paulson and Fairfax are the second-largest shareholders in Piraeus Bank and Eurobank respectively, while Capital Group is among the top five investors in both lenders.

Paulson, the investment firm founded by billionaire John Paulson, disclosed a 6.6 percent stake in Piraeus Bank in the second quarter of 2014, and still held the same amount at the end of March this year, the data show. That stake was valued at about 655 million euros ($737 million) on the date that the investment was disclosed. The shares closed at just 40 cents on Friday, making the same stake worth just 162 million euros, the data show.

Piraeus Bank also sold its 9.9 percent stake in Athens Water Supply & Sewage Co. to Paulson for 86.3 million euros last May, a bank official said.

Investors led by Canada’s Fairfax, which previously made successful bets on Bank of Ireland during the financial crisis, in April last year bought about 1.3 billion shares in Eurobank, according to the firm’s 2014 letter to shareholders. The stake amounts to about 9 percent of the share capital today and is valued at about 191 million euros. The shares are now worth less than half the 31 cents that investors in the share sale paid.

NBG and Alpha Bank haven’t fared much better; their shares have fallen 55 percent and 53 percent respectively in the last 12 months. BlackRock — which has held NBG shares on-and-off for several years — increased its stake to 9.7 million shares in the second quarter of 2014, and again to 90.1 million in the first quarter of this year.

The poor performance means that U.S. funds, the largest foreign source of capital for European share sales, may now hold back from investing in the region. Companies in Greece raised over $12 billion in share sales last year, the highest amount since 1999, according to data compiled by Bloomberg. This year that number is zero.

“The news flow around Greece is creating a lot of volatility that could make it more difficult for U.S. investors to commit to Europe,” said Craig Coben, global co-head of equity capital markets at Bank of America Merrill Lynch.

Spokesmen for Blackstone, Capital Group, Fairfax and Paulson declined to comment. A representative for Fidelity didn’t respond to a request for comment.