The Swiss Market Index (SMI) dropped 1.36 percent to 5,873.84 points in midday trading, its lowest point since December.
"The stock markets could remain under pressure this week and will be sensitive to news from Greece," said analysts at Hyposwiss bank who forecast a Greek exit from the eurozone "sooner or later."
The Zurich Cantonal Bank said meanwhile that the possibility of a new round of elections in Greece could maintain pressure on stocks until mid-June.
Equities sank across Europe on Monday and the euro tumbled to its lowest point since January as Greek president Carolos Papoulias prepared for more talks aimed at breaking a political deadlock.
On May 6th, Greek voters delivered a sharp rebuke to mainstream parties that negotiated a second financial rescue by the European Union and International Monetary Fund, but which imposed tough austerity measures.