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Tesla quarter could be a lemon: Analyst

Tesla is gearing up to report earnings on Wednesday after the close, and according to one analyst, the quarter could end up being a lemon.

Shares of Tesla have climbed around 20 percent so far this year, outpacing auto competitors such as Ford, GM and Toyota. But UBS analyst Colin Langan says the party could be over, particularly if Tesla turns in the kind of quarter he's expecting.

Langan, who downgraded Tesla to "sell" from "neutral" last month, told CNBC's "Fast Money" that he was "cautious" heading into the quarterly report.

"We're cautious heading into the print. We're below consensus, expecting a 67 cent loss compared to consensus of 60 cents, really driven by weaker operating margins," he said.

Langan's primary concerns with Tesla dealt with both the auto and storage segments.

On the auto side, Langan said the company's full-year delivery target of 55,000 vehicles may be too optimistic. "I think that's going to be at risk as they go into the second half as it implies a 50 percent increase from the first half," he said.

Langan also expressed concern over the timing of the Model X launch. "Originally, it was supposed to be Q2, now it's late Q3, we'll see if it stays on schedule," he said. "Clearly, that's going to be an important read for future model launches."

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Still, the majority of analysts are bullish on Tesla, with an average price target of $279.78. It was trading at around $265 before noon Wednesday.

On the storage side, Langan wrote in a recent research note that the pace of early storage orders for Tesla's Powerwall and Powerpack products was "misleading." "Customers did not put down deposits, so these are just solicitations of interest," he wrote.

"More importantly, early adopters … likely are driving up initial orders," he added, "but once these orders are filled, making the mass market leap will likely be difficult."

Because of slow storage growth and delivery concerns, Langan told CNBC he was reiterating his "sell" rating heading into Wednesday's report.