Nike's (NKE) - Get Report third-quarter earnings to be released Tuesday may not be a slam dunk because of slowing sales of basketball sneakers. 

With the popularity of Golden State Warriors guard Stephen Curry spurring sales of basketball kicks for Under Armour (UA) - Get Report , and a broader consumer trend toward wearing casual sneakers, Nike may have come up short during the quarter in a business it has long dominated.

"Nike's signature basketball business in North America has seen a shift to Under Armour's Stephen Curry at the expense of lines from LeBron James, Kevin Durant and Kobe Bryant," wrote Canaccord Genuity analyst Camilo Lyon in a March 21 note to clients.  

Lyon, who rates Nike a hold, believes Nike's basketball sneaker sales slowdown may be causing the footwear giant much larger headaches. "Discussions with our industry contacts suggest there have been management departures in Nike basketball due to stale LeBron product and the commensurate under-performance of recent LeBron 13 launches -- also we believe Nike has been taking back poor-selling LeBron product from retailers."

It's not too hard to find the source of Wall Street's concern about the health of Nike's basketball business, which represents about 13% of Nike's annual sales.

Sales for the Nike basketball division rose by only a mid single-digit percentage in the second quarter ended Nov. 30.  That marked a sharp slowdown from the 21% growth Nike saw in the fiscal year ended May 31, 2015. At Foot Locker (FL) - Get Report , sales of running sneakers surged by a double-digit percentage in the fourth quarter.  But basketball sales only rose by a low-single digit. In the third quarter, Foot Locker's basketball sales gained by a more robust mid-single digit percentage.

"The rumored death of basketball, where our leadership position is most widely recognized, has been greatly exaggerated -- although growth in the basketball category during the quarter was modest relative to running, it was nonetheless growth," said Foot Locker CEO Dick Johnson to analysts on a Feb. 23 call. While Johnson pointed to solid interest in Nike's Kyrie and Air Force 1 basketball lines, he acknowledged a slowdown in most other signature basketball products. 

According to data compiled by SportsOneSource, the basketball sneaker category was the second-largest category in the athletic sneaker market last year, with 22% of the industry's sales, a 0.7% drop from 2014. On the other hand, casual athletic footwear clocked in with 21.3% of industry sales, up markedly from 18.9% in 2014.

The cloudy outlook for such a sizable business for Nike may be weighing on the stock. 

Shares of Nike have fallen 2.9% in the past three months, underperforming the Dow Jones Industrial Average's 2% gain. 

On the positive side, interest in products under Nike's pricey Jordan brand seem to be intact.  

"The Jordan business is exceptionally strong, while the Nike basketball business has been soft -- it's an item issue as [offerings from] Kobe Bryant, Kevin Durant and Lebron James did not do as well last year," said Sam Poser, a veteran footwear industry analyst and managing director at Sterne Agee.