Greece, responsible for 0.4 percent of the world economy, now poses a threat to international prosperity as investors raise bets its days using the euro are numbered.

A Greek departure from the currency would inflict “collateral damage,” says Pacific Investment Management Co.'s Richard Clarida, a view echoed by economists from Bank of America Merrill Lynch and JPMorgan Chase & Co. At worst, it could spur sovereign defaults in Europe as well as bank runs, credit crunches and recessions that may spark more euro exits.

Global trade and financial ties mean the pain wouldn't be confined to the euro area. JPMorgan Chase estimates a 1 percentage point slump in the euro countries' economy drags down growth elsewhere by 0.7 percentage point. Exporting nations from the U.K. to China would suffer and commodity producer Russia would face falling oil prices. While the U.S. may fare better, even it would feel echoes similar to the financial infection following the bankruptcy of Lehman Brothers Holdings Inc.