The company bought an 11.5% stake in Iconix, which owns the Umbro and Lee Cooper brands, and 2.3% of Dick's Sporting Goods which has more than 500 stores in the US.
It said the deals were designed to "build relationships with key suppliers and brands".
Retail analyst Bryan Roberts said the move was a typical "speculative" move by the company to expand its reach.
However, he said it was too early to say whether it was part of a more general move into the US.
Sports Direct said: "The main rationale for these stakes is to allow Sports Direct to hopefully build a relationship and develop commercial partnerships with the relevant parties."
Sports Direct has a strategy of buying shares to "build influence or forge partnerships", said Mr Roberts, an analyst at TCC Global. He gave the examples of stakes taken by Sports Direct in Debenhams and House of Fraser.
The latest acquisition could be "a foot in the door" of the US market, but it was unclear if it was a precursor to more meaningful expansion in the US, Mr Roberts said.
Sports Direct has been through a turbulent period, having been criticised for its employment practices and last week issuing a profit warning.
Discount retailer Sports Direct has taken stakes in two US sports firms.