Not to sound like one of those cheesy horror movies that you see at midnight on TNT, but just when you thought it was safe to come out from under the covers, Greece's most dangerous effect on corporate earnings could be yet to come.

For those of you who don't care much for horror movies, you can relax because there's no blood involved -- but that doesn't mean corporate America won't be in the red. Instead of knife-wielding monsters, U.S. companies may succumb to the mighty dollar as it completes a Zoro-styled "Z" across their chest and brings them to their knees.

OK, so enough with the terrible metaphors -- let's explain why I'm concerned for American multinationals.

Loser by default?
A Greek default seems all but certain at this point. It's not a matter of how it's going to happen, just when. In an article earlier this week, I explored the possible outcomes of a Greek default and what the true costs to most corporations would be. I came to the conclusion that while financial institutions would suffer in the near term, these losses would be contained and very few firms would face any long-term problems.

Well, I also need to admit that there's one factor I failed to include in that article that could be of serious concern to U.S.-based companies that derive a significant portion of their revenue from Europe. If Greece defaults and the European Union is forced to absorb the shock of its sovereign debt, it could very easily cause questions to arise about the validity of the euro as a currency.

Over the past five weeks, the euro has fallen against the U.S. dollar from $1.45 to $1.34 where it is currently valued. It's very plausible to assume a Greek default could cause further erosion in the euro and strengthen the U.S. dollar. Sounds great, right? Not so fast.

Lost in translation
A strong euro and a weak dollar constrain consumer spending in the U.S. but make U.S.-made goods cheaper abroad. U.S multinationals are able to manufacture their products in America, sell their products in euros internationally, then reap the benefits of the currency translation when those euros are converted back to dollars. If the euro suddenly took a dive south, it could spell disaster for companies that have a strong reliance on Europe for their revenue.

For example, in its latest quarterly filing in July, McDonald's (NYSE: MCD) noted that 41% of its revenue is derived from Europe. In that report, McDonald's reported a $0.10 beneficial gain in income-per-share directly derived from favorable currency translations. Other multinationals that have a strong presence in Europe that could see earnings pressure are Procter & Gamble (NYSE: PG), Ford (NYSE: F), ExxonMobil (NYSE: XOM), General Motors (NYSE: GM), and General Electric (NYSE: GE).

This isn't to say that analysts and even investors won't see past these currency translations as superficial, but it gives pessimists even more fuel for the fire. I wouldn't be surprised if earnings estimates begin falling rapidly for U.S. multinationals in line with a falling euro.

Foolish roundup
I'm still sticking with my original thesis that the real cost of a Greek default is negligible, but this is a side effect that could be trying to many long-term investors' portfolios. My advice: Don't chase a name. If earnings estimates fall and stocks begin to contract, play it smart and let those valuations come to you.

What's your outlook on the euro over the next year? Will it be higher, near the same levels it's at now, or decidedly lower? Take the time to cast your vote in the poll and in the comments section below explain what you might do if the euro does head lower.

Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong The Motley Fool owns shares of Ford Motor. Motley Fool newsletter services have recommended buying shares of Procter & Gamble, McDonald's, Ford Motor, and General Motors. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy that lays things out in a simple way everyone can understand.