The group, owned by Newcastle United chairman Mike Ashley, said it had bought a 2.34% interest in Dick's Sporting Goods (NYSE:DKS).
It also acquired an 11.52% holding in Iconix Brand Group, which owns US retail names in the fashion, sports, entertainment and home sectors including Candie's, Bongo, Joe Boxer and Mudd.
"They also help the company to build relationships with key suppliers and brands."
Last Friday, the sportswear retailer warned investors it was no longer confident of meeting its earnings target for 2015.
The company has also attracted controversy for its use of employment practices such as zero-hours contracts.
At the end of last year, the group moved to stem the criticism by announcing that all staff would receive more than the UK minimum wage from the start of the New Year.
Sports Direct employs 5,000 staff at its main distribution warehouse in Shirebrook, Derbyshire - the focus of an investigation by the Guardian newspaper - with 15,000 staff on zero-hours contracts working in its stores.