Under Armour (NYSE: UAA) shares tumbled 5.57% in pre-market trading on Friday following the release of its first-quarter earnings report, which revealed a significant miss on sales expectations. The sportswear giant's quarterly performance has raised concerns among investors about its growth trajectory and market position.

According to the company's report, Under Armour posted quarterly sales of $1.134 billion, falling short of the analyst consensus estimate of $1.154 billion by 1.77 percent. This represents a 4.22 percent decrease compared to sales of $1.184 billion in the same period last year, indicating potential challenges in the company's revenue growth strategy.

Despite the sales disappointment, Under Armour did show some improvement in profitability. The company reported quarterly earnings of $0.02 per share, doubling from $0.01 per share in the same period last year. However, this positive aspect was overshadowed by the revenue miss, as investors appear more concerned about the company's ability to drive top-line growth in an increasingly competitive athletic apparel market.