European Union heads are waiting for the anti-austerity government in Athens to present new economic reform and budget proposals, as Greece and its EU-IMF creditors struggle to reach a debt deal to prevent a default that could have worldwide repercussions.
"I'm not going to predict what the consequences would be," Lew said in an interview with CNN, asked what would happen in the event of a "Grexit."
"It's clear that within Greece the consequence of a failure here would mean a terrible, terrible decline in their economic performance. It will hurt the Greek people, who will bear the first brunt of a failure."
"The reality is that there are impacts on markets. And I don't think anyone should want to find out," he said of the prospect of Greece leaving the eurozone.
"I urge all the parties to be flexible but I think that we're at a moment now where the burden is on Greece to come back with a response that's the basis for reaching an agreement as soon as possible.