The euro crisis has got as many heads as the Hydra. This week bring another involving Portugal.

Last week the euro started falling again—it closed at $1.2907 on Friday but rallied slightly to $1.2951 today—and yields on Portuguese government debt moved up—the 10-year bond closed at a yield of 7.14%–on fears the Portugal is headed down the same road as Greece and Ireland and will need a formal rescue by the European Union soon.

“Soon” may be coming very quickly. The Portuguese government is scheduled to issue its first bonds of 2011 on Wednesday, January 12. The European Central Bank was buying Portuguese debt last week in an effort to push yields below 7% for the upcoming debt issue. That level is critical: Last week Portuguese officials said that the country could not afford to pay more than 7% on its debt over the long-term. (About $12 billion in Portuguese debt matures in April and June and will have to be refinanced.)

Portugal’s Prime Minister Jose Socrates continues to insist that the country will be able to meet its goal of reducing its budget deficit to 7.3% of GDP in 2010. (That would be a decrease from 9.3% of GDP in 2009.) But financial markets aren’t impressed. The Swiss National Bank said last week that it has stopped accepting Portuguese government bonds as collateral for repurchase agreements. Big Portuguese bank stocks dropped to 14 to 17 year lows on Friday.

If you’ve got stomach for the volatility and the risk, the euro debt crisis has created a buying opportunity for stocks of strong exporters with solid balance sheets. A U.S. investor buying euro-denominated shares of, say, a German exporter such as Siemens (SI) gets to pay in stronger dollars for a company that, because of the weak euro, is seeing an increased competitive advantage in global markets.