Banks hike odds on 'Grexit' – now seen most likely

Following Greece's resounding "no" vote in Sunday's referendum, global banks have upped their stakes on the debt-mired nation quitting the euro zone, with a "Grexit" now viewed by many as more likely than not.

Analysts and economists from banks including JPMorgan, Barclays, Unicredit and Societe Generale have upped their forecasts on the likelihood of a Grexit, making it their base-case scenario. The severely weakened banking system is the main concern, with some suggesting a referendum of the Greek people on the country's membership of the euro zone could be the next step in the warring between Greece and its international creditors.

Read MoreWhat next? Markets sink after Greece votes 'No'

"Our base case is that the pressures coming from a dysfunctional banking system in Greece will shorten the time horizon to negotiate a deal to a handful of weeks," said JP Morgan analyst, Malcolm Barr, in a research note on Monday.

"As that pressure builds, there is likely to be a temptation to call a referendum in Greece on euro membership, and for the state to begin issuing IOUs or similar and giving these some status as legal tender. This is a path that suggests to us that there is now a high likelihood of Greek exit from the euro and possibly under chaotic circumstances."

Getty Images

Pro-European Union protesters take part in a rally in front of the parliament on June 18, 2015 in Athens, Greece.

He added that "For now, we would view a Greek exit from the euro as more likely than not."

Economists at Barclays echoed this view, while the chief economist at Unicredit saying the referendum result meant Greece leaving the euro zone was by far the most likely outcome.

"The process may start within days or weeks, but it won't be a smooth ride into a new currency. It'll be chaos with political ramifications," Erik Nielsen said in a note published late on Sunday.

Nearly two-thirds of Greeks voted "no" in the referendum, rejecting a proposal from creditors that would have required more austerity in return for debt relief and possible aid.

Following the vote, Greece's antagonistic finance minister, Yanis Varoufakis, resigned on Monday. Meanwhile, German Chancellor Angela Merkel and French President Francois Hollande are due to meet in Paris later today to discuss a joint response to the referendum result.

Read MoreBye, Yanis, hello Euclid. Can this man save Greece?

Credit ratings agency Standard & Poor's said it was now more likely than not that Greece would leave the euro, while economists at Societe Generale said there was now a 65 percent probability of a Grexit.

"Avoiding a Grexit is possible, but will be difficult," said Michel Martinez, Societe Generale euro area economist, in a note.

A Grexit is not yet viewed as the "base case" by UBS's chief investment office. However, Themis Themistocleous, the bank's CIO for Europe, the Middle East and Africa, did say that the risk of an exit had increased dramatically in light of the "no" vote.

"We haven't taken it into a base case yet – we want to see how the Europeans react. We have to take a step back little bit, because the logic of a deal is still there," he told CNBC.

"The most likely path to a Grexit is if the banks stay closed, they run out of liquidity and then what happens to the banks? The economy is becoming a cash economy. No economy can function these days without banks. The only way to recapitalise the banks is to issue your own currency. Once you issue your currency, you are out of the euro – that is the most likely way things will play out."

Read MoreMohamed El-Erian: Grexit 'high probability'

Follow us on Twitter: @CNBCWorld