Citigroup Inc. said there's now a 90 percent chance that Greecewill leave the euro in the next 12 to 18 months, with prolongedeconomic weakness and spillover for the currency bloc.

In an analyst note, Citigroup updated its forecast for a Greekexit from the 17-nation currency union from a previous estimate of50 percent to 75 percent, and said it would most likely happen inthe next two to three quarters. Specifically, the bank assumes aGreece exit would occur on Jan. 1, 2013, while saying that is not aforecast of a precise date.

Greece's so-called troika of international creditors, theEuropean Central Bank, the European Commission and theInternational Monetary Fund, are in Athens this week amid doubt thecountry will meet its bailout targets and reluctance among Germanyand other euro-area states to put up more funds should Greece failto do so.