Several European banks are being closely monitored by the agency responsible for closing lenders which go bust in the euro zone.
But none of these banks are failing or about to fail, the head of the Single Resolution Board (SRB) said today.
Elke Koenig did not mention any EU country by name but told the European Parliament's economic affairs committee the SRB was studying a number of banks in "shaky waters".
Since the 2007-09 financial crisis, the EU has adopted rules to shield taxpayers from having to bail out lender again and attention in the single currency bloc has been focused on Italy's plans to bail out two regional banks.
This has posed a dilemma for European regulators who are still considering whether another, bigger Italian lender, Monte dei Paschi di Siena, qualifies for state aid.
"So far we are in a position that we have to conclude that banks might be having quite some challenges ahead of them, but they are not failing or likely to fail," Koenig said.
Germany's Sven Giegold said there were doubts that the European Central Bank, which supervises euro zone lenders on a day-to-day basis, was being tough enough in dealing with banks struggling with poorly performing loans.
Italian lenders in particular are burdened by large amounts of so-called non-performing loans.
Koenig declined to comment on individual banks, but said: "There are a number of situations where we have a very close eye on... It's a number of cases. It's not just one or two."
Earlier she said most banks across the sector were not in such a position that their failure would endanger financial stability.
Koenig also called for banks to be given time to issue debt that can be written down to replenish capital that has been burnt out in a crisis, and thus shield taxpayers.
The biggest banks, such as Deutsche Bank, HSBC and BNP Paribas must begin building up this debt from 2019.
However, the total shortfall for euro zone lenders is between €100 and €200 billion, and the bloc's European Banking Authority has said markets will not be able to absorb such amounts of new debt issuance quickly.
"There needs to be sufficient time," Koenig said.