Greece’s four main banks need to find another €14bn (£10bn) of reserves to ensure they could withstand an economic downturn, the European Central Bank said on Saturday.

The four banks – Alpha Bank, Eurobank, NBG and Piraeus Bank – have until 6 November to say how they intend to make up that shortfall, the ECB said.

The money could come from private investors or from EU bailout funds.

An ECB stress test known as a “comprehensive assessment” identified a capital shortfall of €4.4bn under a best-case scenario and €14.4bn in a worst-case situation.

The shortfall is smaller than originally feared, with the most recent bailout deal setting aside up to €25bn to prop up Greece’s banks.

The ECB audit examined the quality of the banks’ assets and considered the “specific recapitalisation needs” of each institution under Greece’s EU bailout.

“Overall, the stress test identified a capital shortfall across the four participating banks of €4.4bn under the baseline scenario and €14.4bn under the adverse scenario,” the ECB said.

“The four banks will have to submit capital plans explaining how they intend to cover their shortfalls by 6 November. This will start a recapitalisation process under the economic adjustment programme that must conclude before the end of the year.”

Increasing the banks’ capital reserves would “improve the resilience of their balance sheets and their capacity to withstand potential adverse macroeconomic shock”, the central bank added.

In August, eurozone finance ministers released €26bn of the €86bn in bailout funds that went to recapitalising Greece’s stricken banking sector and make a debt payment to the ECB.

Greek banks have already been bailed out under earlier deals for the country. They suffered further losses as Greece headed towards a third bailout earlier this year.

Depositors pulled billions out of the country fearing that Greece would be forced to leave the euro. Limits on withdrawals and transfers imposed in June to prevent Greek banks from collapsing remain in place, although they have been loosened.