The current bailout, which has already been extended by two months, runs out at the end of February. Athens had hoped to replace it with an Enhanced Conditions Credit Line (ECCL) from the euro zone bailout fund that it would never have to use.

"There will have to be an extension beyond February. It will be inevitable," one euro zone official with knowledge of the talks said. "It could be six months more."

The extension would have to be requested by the new Greek government that emerges after elections on Jan. 25.

But with Greek borrowing costs skyrocketing on uncertainty about policy after the elections, Athens looks set to need further euro zone support and a credit line for insurance purposes only may not be enough, euro zone officials said.

Also, without another programme, under which Greece gets cheap euro zone loans or access to a credit line in exchange for reforms, the European Central Bank said it could not provide liquidity to the Greek banking sector.

No decisions were taken and the issue is likely to be further discussed at the next meeting of euro zone finance ministers on Jan. 26, a day after the Greek vote.

"The ECCL is for a country which has in principle market access, and the ECCL is an insurance policy to calm any remaining doubts in the market," a second euro zone official said.

"With some goodwill you could say that towards the end of last year, this could apply to Greece. Now with the uncertainty, stress on the financial system, Greek long-term yield going beyond 10 percent - all that makes it much less obvious Greece qualifies for an ECCL," the official said.

"The entire Greek situation looks less favourable than six weeks ago. What they would need is just a normal programme," the official said, adding that Greece could need a programme extension of five to six months.

There was no discussion among the officials preparing the ministerial meeting of any amounts of a potential third bailout or any other details.

"It was brainstorming, the discussion was about scenarios rather than any concrete decisions," the first official said.

Another source of concern was the outflow of Greek bank deposits, which the first official said was at about 60 million euros a day.

The deposit outflow was among the reasons why two major Greek banks, Eurobank and Alpha, have applied to tap the national central bank's emergency funding a year after ending their reliance on it.

Euro zone officials said the deposit outflow undermined the source of funding envisaged for the Greek credit line - the 10.9 billion euros in the Greek bank stability fund, the HFSF, left over from a recapitalisation loan for Greek banks.

After the ECB's asset quality review and stress tests last year, Greek banks were declared in the clear and euro zone finance ministers wanted to re-use some 10 billion of the HFSF money as the new precautionary credit line, leaving roughly 1 billion in for emergencies.

"It now looks like it is more prudent to keep more money in the HFSF," the second euro zone official said.

A Greek finance ministry spokesperson declined to comment.

(Additional reporting by Lefteris Papadimas in Athens; Editing by Hugh Lawson)

By Jan Strupczewski