"Heightened geopolitical risk and the prospect of U.S. and EU economic sanctions following Russia's incorporation of Crimea could reduce the flow of potential investment,trigger rising capital outflows, and further weaken Russia's already deteriorating economic performance," S&P argued.
What might be more concerning for Russia is that Russian investment firm Renaissance Capital, usually one of the more positive voices on the Russian economy, downgraded its forecasts for economic growth for 2014 from 3.3 percent to 1.6 percent. The country's gross domestic product will shrink in the first quarter rather than growing, according to Renaissance's leading indicator. And their projections are based on the assumption that an agreement will be reached soon on Ukraine's future.
(Read more: EU ready to step up sanctions on Russia)
"We believe a compromise on Ukraine will be found sooner or later, and that increased sanctions against Russia are unlikely," its economists argued.
Since the crisis in Ukraine erupted, Russia has seen a plummet in the value of its currency, investors yanking their money out of its stock market and downgrading of its growth prospects. With further sanctions on the cards, the party in Crimea may be followed by a horrible hangover.
- By CNBC's Catherine Boyle. Twitter: @cboylecnbc.