FRANKFURT — No matter which way the Greek vote goes, the European Central Bank on Monday will face a series of agonizing decisions. Greece’s future in the eurozone may well depend on how far the central bank is willing to go to prop up struggling Greek banks and prevent a total economic collapse.

If Greeks vote yes — agreeing to accept unpopular dictates from other eurozone nations and international creditors in return for more aid — the central bank would have a much easier time justifying emergency loans and other steps to keep the banks from failing. No economy can function properly without banks; if they topple, so will the economy.

But if Greeks vote no, Mario Draghi, the president of the E.C.B., may be confronted with a difficult choice. The central bank’s rules would probably require it to stop providing cash to Greek banks. But Mr. Draghi might be tempted to find a way around those rules, because choking off financial support would thrust untold hardship upon ordinary Greeks and might send the country on its way out of the euro currency union.

Either way the situation is tricky, and there are no precedents to rely on.

“It’s fair to say we can expect a few surprises in the next few days,” said Nicolas Véron, a senior fellow at Bruegel, a research organization in Brussels. “Clearly, we are in uncharted territory.”