Three eurozone nations will likely have to restructure their government debt next year, and Greece will probably exit the currency, according to Michael Saunders, Citigroup’s chief European economist.

"In Europe, we assume that in the near term, as recently, creditor nations will do just enough — through official support — to prevent [the European Monetary Union from] disintegrating, but not enough to return the periphery countries to sustainable fiscal paths," he wrote in a report obtained by CNBC.

"Eventually, we expect Grexit [Greece’s exit from the eurozone] and a series of sovereign debt restructurings, alongside moves towards tighter integration among EMU countries."

Editor's Note: The ‘Unthinkable’ Could Happen — Wall Street Journal. Prepare for Meltdown

Saunders anticipates that Italy, Spain and Greece will need debt restructurings next year, and the same will be true of Ireland, Portugal, Cyprus and Slovenia by 2017.

Despite the eurozone’s recent re-entrance into a recession, financial market participants have remained calm. "Investors could clearly be too optimistic at this point," Saunders said.

Eurozone gross domestic product shrank 0.1 percent in the third quarter.

Eurozone finance ministers and the International Monetary Fund agreed Monday on a new debt target for Greece, but the euro gained only a little afterward.

"It was not a huge reaction because [the deal] was already priced in," Joseph Capurso, a currency strategist at Commonwealth Bank of Australia, told Reuters. "Economic data in Europe is getting worse.”

Editor's Note: The ‘Unthinkable’ Could Happen — Wall Street Journal. Prepare for Meltdown