Shares of Shake Shack (SHAK) - Get Shake Shack, Inc. Class A Report are off session lows, but the stock is still down about 2.1% to $45.25 on Friday.

What's got the stock down and why did Shake Shack fall more than 5% at the open? Simple: a downgrade. Jefferies analyst Andy Barish slapped Shack Shack with an underperform rating and a $36 price target. As of Thursday's close, that implied almost 22% downside in the New York City based burger company.

Some of the hometown fans may not be too happy to see Barish's take, although he's not knocking the company's long-term potential. In fact, Barish says he still believes that Shake Shack has a bright future. However, even with Friday's fall, Shake Shack stock is still up more than 45% since September 1st.

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"Much of that [potential] is already discounted in the current valuation," he contends. In essence, he's calling the stock overvalued based on its current business given the run in the share price.

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Barish also makes the point that traffic will likely be negative in 2018, due to "store cannibalization, high volumes and a small comp base."

Will Wall Street respect that call or will investors continue to bid the stock higher? While we don't know the longer-term implications, we can see that there's a bit of a debate already on Friday. While shares are down on the day thanks to the analyst's call, it's off the lows by quite a bit.

Let's see how Shake Shack stock trades through the holiday-shortened week after Christmas.

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This article is commentary by an independent contributor. At the time of publication, the author had no positions in the stocks mentioned.