Warner has secured the rights to license, manufacture, distribute, promote and sell club-branded merchandise throughout the Americas. As well as United, the deal also includes Juventus and Paris St Germain.
The planned product range includes clothing and accessories, toys and games, homewares, stationery, gifts and collectible items.
Warner said the popularity of football in the US continues to soar on the back of the World Cup, in which every match was shown live, and increasing numbers of pre-season tours by European clubs.
Warner Brothers Consumer Products, which is a subsidiary of media giant Time Warner, also represents AC Milan, the Mexican national team and the 2008 Uefa European Championships.
Jordon Sollitto, executive vice-president of international licensing and new business initiatives, said: "Football merchandising is a fast growing business for us and nowhere is the going forward opportunity more exciting than right here in the US."
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