Coca-Cola is buying a minority stake in a sports drink brand backed by basketball star Kobe Bryant, it said on Tuesday, seeking to mount a stronger challenge to top energy drink Gatorade.

The investment in BodyArmor comes as Coke's Powerade steadily cedes market share to its more popular PepsiCo-owned rival. Coke has also been rattled by falling demand for its fizzy colas.

The company did not disclose the size of the investment or other financial details, but said it could increase its ownership stake in BodyArmor.

Bryant is BodyArmor's third biggest shareholder and also has endorsement deals with baseball player Mike Trout and another NBA star, James Harden.