Tesla's disappointing Model 3 production ramp is a troubling sign, according to one Wall Street firm.

UBS reaffirmed its sell rating on the electric car maker's shares, predicting Tesla will continue to have issues producing its Model 3 vehicles.

In the third quarter, Tesla delivered 26,150 total vehicles and just 220 Model 3 cars versus the FactSet estimates for 25,860 and 1,260, respectively. Two months before Tesla revealed the numbers, it had said it would produce 1,500 Model 3 vehicles for the quarter.

"Not only does the [Model 3] miss undermine the credibility of future Model 3 targets, but it increases the near term risks," analyst Colin Langan wrote in a note to clients Monday. "We believe the market should not ignore fundamental challenges that persist with regards to Tesla's Model 3 profitability, stationary storage & solar businesses, and eventual need to raise cash."

Tesla's stock traded down slightly Monday morning. Its shares are up 50 percent this year versus the S&P 500's 15 percent gain through Friday.

Langan reiterated his $185 12-month price target for Tesla shares, representing 42 percent downside to Friday's close.

The analyst lowered his financial results estimates for the company due to the "slower Model 3 ramp." He reduced his Tesla results forecast to a loss of $6.40 per share from a loss of $5.30 for 2017 and to a loss of $3.30 from a loss of $1.60 for 2018.

"With limited Model 3 profitability, infrastructure expansion needs, & Model Y capacity build (late 2019), we believe TSLA will eventually need additional outside funding," he wrote. "We see increased pressure on demand as luxury automakers launch competing products in the 2018-20."

Tesla did not immediately respond to a request for comment.

— CNBC's Michael Bloom contributed to this story.