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

What: Shares of Infinera (NASDAQ:INFN) climbed about 5% in premarket trading Wednesday after Goldman Sachs upgraded the optical networking technologist from neutral to buy.

So what: Along with the upgrade, analyst Simona Jankowski planted a price target of $11.50, representing about 36% worth of upside to yesterday's close. While momentum traders might be turned off by the stock's weakness in recent months, Jankowski's call suggests growing sentiment on Wall Street that Infinera is now too cheap to pass up. 

Now what: According to Goldman, Infinera's risk/reward trade-off is particularly attractive at the moment. "We believe consensus is underestimating the revenue growth potential associated with customer upgrades and market share gains in 100G long haul, which is forecast to grow at nearly a 40% CAGR through 2015," said Jankowski. When you couple that upbeat outlook with Infinera's solid balance sheet and sluggish stock price, it's tough to disagree with Goldman's upgrade.

Editor's Note: The previous version incorrectly identified Goldman's analyst call as a downgrade. This version has been corrected and The Motley Fool apologizes for the error.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.