Cramer: This is my main concern about Nike

Nike investors should be most worried about the excess inventory the apparel giant reported for last quarter, CNBC's Jim Cramer said Wednesday.

"When people see excess inventory, what they think of is Steph Curry, they think Under Armour," Cramer said on CNBC's "Squawk on the Street." "What [Under Armour CEO] Kevin Plank has done is pick the right guys."

Under Armour last year extended its contract with the NBA superstar through 2024, and signed golf sensation Jordan Spieth to a 10-year deal.

Nike reported mixed quarterly results on Tuesday, with earnings per share beating expectations, but revenues missing forecasts. Nike also said its inventories grew by 8 percent last quarter.

"We have been working to efficiently clear excess inventory in North America and we have made good progress on Q3," Nike Brand President Trevor Edwards said on the company's conference call.

Under Armour shares are slightly outperforming Nike's this year, but Nike has risen over 20 percent in the last year, while Under Armour is only up 2 percent.

Nike (blue) vs. Under Armour (green) in last yearSource: FactSet

Disclosure: Cramer's trust did not own Nike or Under Armour stock when this article was published.