Since L Brands said its Victoria's Secret brand would stop selling swimwear and dial back on promotions, the company's shares have plunged as steeply as one of its asset-baring bras.

But one analyst fears the retailer's woes may extend beyond this shift in strategy — meaning a recovery in its stock price could take longer than expected.

Jefferies analyst Randal Konik on Monday downgraded L Brands' shares from hold to underperform, saying industry and consumer trends could cause Victoria's Secret to lose its dominance in intimate apparel. Among those trends are a slowdown in spending on the category and increased competition from specialty stores and online start-ups.

But perhaps more importantly, Americans are moving away from the "bombshell" look Victoria's Secret has built its reputation on, and are instead stocking up on more natural, unstructured bralettes. Because bralettes are easier to construct, they make it simpler for nontraditional lingerie brands to challenge the stalwart. Both American Eagle's aerie lingerie line and Urban Outfitters have recently cited the item as one trend fueling their sales.

"We believe the growth in popularity of bralettes is reflective of a broader shift in the consumers' mindset, particularly among younger consumers, which are increasingly rejecting traditional beauty standards in favor of more natural, attainable looks," Konik told investors.

The analyst pointed to a decline in breast augmentations as one example of consumers' changing tastes. Roughly 279,000 American women went under the knife in 2015, down from nearly 331,000 three years earlier. It was the third consecutive year that number had fallen.

And in its December issue, Vogue UK declared that showing cleavage is no longer fashionable.

