Italian banks on Friday bore the brunt of concerns about the financial health of Europe's banking sector before official results of stress tests due on 15 July.

Britain's big banks – including bailed-out Royal Bank of Scotland and Lloyds Banking Group – are among 91 in Europe to have been subjected to the crisis scenarios drawn up by the European Banking Authority.

While Britain's banks are expected to pass the health check, Italian bank shares slumped amid concern they might need new capital and that the country may be dragged into the eurozone crisis.

Ratings agency Moody's has already predicted that almost a third of the banks being tested might need some form of external support to bolster their capital.

The focus turned to Italy on Friday when shares in the country's biggest bank, UniCredit, were temporarily suspended amid anxiety it might need to raise fresh capital. It is the only major Italian bank that has yet to do so.

Italian officials insisted the stress tests would not be an issue for the country's banks. Even so, Italy became caught up in the anxiety about the health of the banking system and the eurozone. The premium that investors demand to hold Italian rather than benchmark German bonds reached its widest level since the launch of the euro more than 10 years ago.

M&G's Mike Riddell noted that Italy was now in the sights of speculators and described the situation as a "bloodbath".

"Italian 10-year bond yield spreads have widened by 25 basis points versus Germany to a euro-era record. Long-dated Italian government bonds fell as much as 2 points earlier today," he said, noting that it costs Italy 4.6% if it wants to borrow for five years, and 5.3% if it wants to borrow for 10 years.

Among the concerns is that governments might have to prop up banks again if they fail the stress tests. According to Reuters, a document circulating in Brussels gives banks until the end of September to show how they might find the extra capital and then another three months to raise it, before governments step in.

According to the reports, banks would be asked to first find "private-sector measures, including ... retained earnings ... [and] raising additional common equity or high-quality hybrid instruments from private investors, asset sales [or] mergers" before the authorities intervened.

The tests are conducted by national regulators across Europe but compiled by the European Banking Authority, which requires banks' crucial core tier one capital to remain above 5% after at least one of the worst-case scenarios, which include a drop in GDP over two years of 4%, compared with 3% for last year's tests.

There has been some concern that the authorities are determined that some banks fail the tests after the farce of last year, when Ireland's banks were given a clean bill of health four months before they were bailed out.

Analysts at Nomura said that the largest capitalised banks in Europe were stronger than their global peers and they believed the tests were credible. "We expect a few failures," the analysts said.