Difficult times for Chipotle shareholders will not turn around anytime soon, according to one Wall Street firm.

Cowen reiterated its underperform rating on Chipotle shares, predicting the company's fourth-quarter sales will come in below expectations.

"If Facebook check-in's are indicative of traffic, data suggests the most recent weekly trend weakened to the softest levels of 4Q," analyst Andrew Charles wrote in a note to clients Friday. "If 4Q same store sales fall below consensus expectations, we believe Chipotle will have difficulty credibly guiding 2018 comps to a level in-line with consensus forecasts absent a significant improvement in January traffic."

Charles reiterated his Chipotle fourth-quarter comparable sales growth estimate of zero percent versus the Wall Street consensus of 1.4 percent.

The analyst said the firm's analysis of Facebook check-in data revealed weaker traffic trends in the latter part of December. Facebook check-ins refer to when "users physically visit a restaurant and tag Chipotle as 'Have Visited/Were Here,'" according to the note.

"We note the most recent five days' -52.2% represents the weakest stretch of five day check-in growth in 4Q, with 12/27/17 (most recent date available) serving as the softest day of year/year check-in growth in 4Q at -56.4%," he wrote.

Charles also reaffirmed his $240 price target for Chipotle shares, representing 19 percent downside from Thursday's close.

The company's stock has significantly underperformed the market this year. It is down 22 percent year to date through Thursday compared with the S&P 500's 20 percent gain.

Chipotle did not immediately respond to a request for comment.

