Shares of Chipotle Mexican Grill (NYSE:CMG) closed below $400 on Tuesday. That's a rare sight in recent months, but we've been here before. We saw Chipotle stock close below $400 in back-to-back days in February, followed by a one-day dip in mid-March. 

Monday's sell-off was triggered by a cautious analyst note. Brian Bittner at Oppenheimer, who has a neutral "perform" rating on the stock, isn't viewing Chipotle's recent 20% retreat as a buying opportunity. Comps have turned positive, and anecdotes suggest that lines are starting to get long again during peak dining periods. The real challenge in Bittner's eyes will be next year, when Chipotle's comps will be stacked against this year's unit-level growth spurts. 

Interior of a Chipotle in California.

Image source: Chipotle Mexican Grill.

Chips off the old guac

Oppenheimer's Bittner is certainly correct in sizing up Chipotle's recovery as a work in progress. The chain's 17.8% spike in comps during the first quarter may have turned heads, but it's not even half of the bounce that store-level sales have to generate to get the burrito roller back to peak 2015 levels. Comparable-restaurant sales plunged 29.7% during the prior year's first quarter, and cruel math dictates that you need to grow 42% to claw your way out of a nearly 30% hole. It will be hard for Chipotle to return to peak form next year in terms of individual restaurant sales, and that's before we even consider what's been happening with margin erosion. 

Costs are rising at Chipotle, and lately that's included ramping up marketing budgets to woo back the hungry. Folks are coming back to Chipotle, but the bottom line has been slower in coming around. Revenue should hit record levels this year, given Chipotle's brisk expansion over the past two years, but net income is another story. Analysts don't see earnings per share approaching 2015's results until 2019 at the earliest. 

A lot can go wrong between now and 2019, and that's led to more than just Bittner taking a wait-and-see approach. Analysts at Maxim, Credit Suisse, and Deutsche Bank put out cautious notes last month after an SEC filing suggested that operating costs as a percentage of sales will move sequentially higher during the current quarter. 

Chipotle announces second-quarter results in two weeks. The stock's unlikely to take off again until we see where Chipotle stands at that point. Customers are coming back, but jaded investors are holding out for a recovery on both ends of the income statement.

Rick Munarriz has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Chipotle Mexican Grill. The Motley Fool has a disclosure policy.