Although financial markets may not yet have found a new equilibrium since the post-referendum turmoil, Dombret warned euro zone countries against using the volatility as an excuse to circumvent bank regulations, particularly bail-in rules.
"If we allow states to provide discretionary aid to their banks, this impedes a core element of the bail-in regime, namely its credibility," Dombret said. "If the bail-in mechanism were to be exposed or even dismantled, markets would no longer exert their disciplinary function."
The comments appear to be directed at Italy, which has been in talks with the EU to provide state aid to its troubled bank sector, weighted down by 360 billion euros ($400 billion) of non-performing loans.
Italy's chief concern is that recapitalization could require banks to bail in investors, who include ordinary households, making any restructuring politically painful.
ECB policymakers have argued that state aid, particularly in case of systemic risk may be acceptable but the bail-in rules must be respected.
The compromise may be government compensation for small investors but euro zone finance ministers threw cold water on the idea on Monday when they argued there was no acute crisis and a bank-by-bank solution was needed.