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 Panera Bread (NASDAQ:PNRA) sank 2% today after Morgan Stanley downgraded the bakery-cafe operator from overweight to equal-weight.

So what: Along with the downgrade, analyst John Glass removed his price target on the stock of $190 per share, suggesting that he sees very limited upside in Panera right now. Glass is particularly concerned that the company's same-store sales are slowing amid intensifying competition from less expensive rivals, prompting investors to lower their valuation estimates on the stock.

Now what: Glass lowered his EPS estimates to the low end of Panera's 2013 guidance and below the Wall Street consensus for 2014. "While check growth is a complex combination of pricing, mix, and catering, it is clear from our survey work that value is a perceived weakness in an otherwise sterling brand," said Glass. "One third of [Panera] consumers indicate that menu prices are high, which we think lowers frequency." With the stock flirting with its 52-week lows once again and trading at a reasonable forward P/E of 20, however, the growth that Panera does have left might be available on the cheap.

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