Not much worse, frankly. The banks are illiquid: they aren’t able to convert their assets (mostly loans) into the cash that their creditors (mostly depositors) are demanding. The only entity that had been providing this liquidity, by lending the banks emergency cash, had been the Greek central bank. But the European Central Bank has frozen that emergency lending.
The result is that the banks have shut down: They are dribbling their last remaining cash out to depositors, who are limited to €60 ($66) per day. They have stopped making electronic transfers of euros overseas.
In effect, Greece already has one foot outside the eurozone: Businesses and consumers in the country now prefer cash. A euro in a Greek bank account is not the same as a euro in cash or a euro in a German bank account. In effect, Greeks believe that the “currency” in their accounts is not really euros.