Updated with comments from Jim Cramer.

NEW YORK ( TheStreet) -- It may be tough for mighty Nike (NKE) - Get Report to admit, but some U.S. consumers are starting to run towards competitor's offerings in one of its key businesses.

That business is running sneakers priced under $100, a market segment that the Oregon-based powerhouse has long dominated. In fact, Nike was founded in 1964 on its ability to sell a better running shoe at a reasonable price.

According to Nike's third quarter 10-Q filing with the SEC, which covered the period ending Feb. 28, 2015, sales of running footwear declined. The company pinned the blame on a sales drop in North America stemming from "lower sales of entry level products."

A large fraction of those entry level products a sneakers from Nike's Roshe Run line, which often retail for below $100. On the other hand, Nike said its higher-priced, performance running styles, such as those using its Flyknit technology, continued to sell briskly. Shoes in that category generally sell for around $119 to $149 a pair.

Going back to Nike's fiscal second quarter, Nike also appeared to be having problems selling cheaper running shoes due to improved styles from Under Armour (UA) - Get Report, Adidas, Puma and Reebok. At that time, Nike said in its SEC filing that sneakers using technologies such as the Nike Free, Max Air, Lunar, Zoom Air and Flyknit lines helped to drive a 21% sales increase in footwear, excluding the impact of currency. Nike did not break out the performance in its North America running shoe business at that time.

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The weakness in what Nike calls its "core running" categories was discussed in its most recent earnings call in March. "Core footwear, within the running category, isn't performing as well as we would like, particularly in North America," admitted Nike brand President Trevor Edwards.

Later in the call he added, "We think there's opportunity for us to do better in that zone," and pointed to Nike's need to bring more innovation to get its offerings back up to snuff. Bringing new styles and technologies to market quickly could halt this rare marke-share loss in the running business for Nike.

According to data from research firm NPD Group, Nike's share of the North American running business declined 0.2% to 57.9% through May of this year, while Under Armour's market share has risen to 3.5%, from 2.8% in 2014. Adidas' share in running has also surged, going to 4.8% year to date from 3.4% last year.  

"It's clear other brands have cut into Nike's running sales a little bit," said Sneakernews.com managing editor John Kim. Nike, said Kim, is focusing more on running styles priced in the $110 to $200 range, and doesn't have much on offer below $100, which has left the door open for rivals to grab some sales. "Nike is still dominating though," said Kim.

Investors will likely be seeking better results from the running business when Nike reports earnings on Thursday evening, especially as the company signaled confidence in its product development pipeline for the next 18 months.

"I don't like that Nike has run up so much," said TheStreet's Jim Cramer, Portfolio Manager of the Action Alerts PLUS Charitable Trust Portfolio. "Otherwise the quarter should be good."

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Overall, Nike's running business, which includes apparel as well as footwear, represents about 19% of the company's annual sales. So getting sales in North America headed in the right direction is critical, especially since Nike shares are being valued at a considerable premium to the Dow Jones Industrial Average and S&P 500. Nike's forward price-to-earnings ratio is a lofty 27, versus 15 for the Dow and 18 for the S&P 500. 

But even as Nike tries to reverse its sales declines of affordable running sneakers, several rivals are taking aim at its dominance in premium running shoes.

Under Armour's $130 SpeedForm Gemini running shoe line, for example, is popping up more and more on the websites of sneaker retailers Foot Locker (FL) - Get Report and Finish Line (FINL) . According to Under Armour execs in April, the Speedform Gemini line is "reviewing well" among consumers and selling well at retailers.

For Adidas' running business, sales have risen by a double-digit percentage for four straight quarters. Sales gained 17% in the most recent quarter alone, based on the success of Adidas' new Boost technology, which features enhanced cushioning for runners. Shoes using Boost technology cost as much as $159 a pair. 

In February, Adidas unveiled its ultra-boost technology (pictured above), which it believes is "its best running shoe ever." Adidas sees itself doubling sales of Boost-related shoes in 2015 to about 7 million pairs.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.