While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a look at particularly stock-shaking analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of MasterCard (NYSE:MA) slipped about 1% this morning after FBR Capital downgraded the credit card giant from outperform to market perform.

So what: Along with the downgrade, analyst Scott Valentin planted a price target of $82 on the stock, representing about 8% worth of upside to Friday's close. While contrarians might be attracted to MasterCard's earnings-related plunge last week, Valentin thinks the appreciation potential remains limited given the several headwinds working against the company.

Now what: FBR lowered its 2014 earnings-per-share estimate for MasterCard from $3.13 to $3.03, and its 2015 view from $3.76 to $3.65. "The downgrade reflects our concern regarding MasterCard's exposure to potentially slowing emerging market economies, along with increased currency volatility, having a negative impact on MasterCard's results and investor sentiment," Valentin noted. "APMEA and Latin America comprise 37% of MasterCard's [gross dollar volume], and while posting strong current GDV growth rates, we believe they have the potential to slow."

With MasterCard shares off 10% over just the past month, however, those concerns might be providing patient Fools with a high-quality value opportunity. 

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Brian Pacampara has no position in any stocks mentioned. The Motley Fool recommends MasterCard. The Motley Fool owns shares of MasterCard. 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.