For athletes in Center City, options to purchase activewear are shrinking.

The Under Armour store at 1529 Walnut St. appeared to shut down over the weekend. In a statement, the company confirmed the closure but provided few other details.

"As part of our omni-channel strategy, we continually seek to optimize global operations," the statement said. "Based on this thorough process, we have decided to close our Philadelphia (Walnut Street) location."

The store opened about two years ago, in August 2016. With the closure, Under Armour is following in the footsteps of other national retailers, such as Armani Exchange and Nine West, that have left Philadelphia's shopping district within the last year. Store closures have been a cause for concern for the future of Center City's upscale shopping district.

>> READ MORE: Like yesterday's fashion, has Center City's retail revival been discontinued?

As the Inquirer reported last year, not only have a variety of luxury retailers left the Center City shopping district over the past few years, but the vacancies left behind are increasingly difficult to fill.

One such vacancy now exists in the Beacon, where the Walnut Street Under Armour was housed. A 15-story structure built in 1926 and owned by Pearl Properties, the Beacon is also home to 98 luxury apartments. Pearl Properties declined to comment.

The space within the Beacon that housed Under Armour is a 10,000-square-foot corner property, which is more valuable than a mid-block site. It's been reported that a retailer at a coveted corner store between the 1400 and 1700 blocks of Walnut Street, a prime shopping strip in Center City, could expect to pay around $185 to $200 per square foot in 2017.

The last two years have been inconsistent for the Under Armour brand. In the time period Under Armour has operated in Center City, the company's stock hit a high of $38.76 per share in August 2016 and a low of $10.59 in October 2017.

Although performing well internationally, Under Armour has been struggling in North America and announced a restructuring plan last year.

The Baltimore-based company's first-quarter results released in May said its North American revenue saw a 1 percent decrease, although total revenue increased by 6 percent. Under Armour chairman and CEO Kevin Plank appeared confident at the time, saying in a statement that the results "demonstrate measured progress" as the company works to "continue to build" its global brand.

Currently, Under Armour's stock is experiencing an uptick, with shares closing at $22.81 Wednesday.