The world's third-largest cement producer's disclosure yesterday that its derivatives position has slid into negative territory drove the stock down 20% in just one day. So is Cemex’s (NYSE:CX) foundation crumbling in for good?

Cemex revealed that its derivatives position on September 30 was a positive U.S. $100. However, as a result of the recent high volatility in the foreign exchange and equity capital markets, the aggregate mark to market has fallen approximately to a negative U.S. $500 million.

The company will report its quarterly results on October 21, and it is vulnerable to concerns that its exchange-rate and interest-rate derivative positions could be hurt by a slide in the peso. In addition, its share price probably has been affected by a Citigroup (NYSE:C) downgrade, predicated on concerns about a slowing U.S. economy.

The yield on the company's credit default swaps also moved substantially higher on Thursday, indicating a concern that it will have difficulty paying the $7 billion in debt it has coming due next year. In light of these concerns, Cemex took the opportunity in its prepared statement to "assure the market that our business model continues to be intact and the capital structure of the company remains unchanged." It also noted that it had "slightly exceeded our guidance for (the) third quarter."

This certainly isn’t the first major slide we’ve seen from Cemex. The company’s shares have been cracked in half since the beginning of October. And Cemex is neither the only big Mexican company nor the lone cement producer to have suffered a share-price slide of late.

Shares of America Movil (NYSE:AMX), the Mexican telecom company, have fallen by about a third thus far in October. At the same time, shares of U.S.-based cement and building materials manufacturers Texas Industries (NYSE:TXI), Eagle Materials (NYSE:EXP), and Vulcan Materials (NYSE:VMC) have experienced October slides of 32%, 28%, and 21%, respectively.

So, what should Fools do with Cemex at this juncture? If you own shares in the company, don’t bow out just yet. After all, this worldwide enterprise currently sports a forward P/E below 4.0. The near term may be wobbly, but as the economic world begins to solidify, Cemex will present investors with a substantial opportunity.

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