Both The Wall Street Journal and Reuters reported that Ackman's vehicle announced the stake, which was first acquired in October, at an dinner for the fund's investors Thursday evening in New York. However, each report indicated that Ackman is happy to be a passive investor in the Beaverton, Ore-based group as it looks to close the gap on rival Adidas AG (ADDYY) in both domestic and international markets.
Nike shares rose 1% early Friday to $68.32, a move that takes the stock's gains since October to more than 30% and gives it market value of $110 billion.
Adidas shares, by contrast, have fallen 4.5% over that time, thanks in part to a surge in the euro.
Nike has faced a significant challenge from Adidas of late, with the German sportswear giant seeing North American sales top the $1 billion mark over its last fiscal quarter as it continues to steal market share and expand its brand in China.
Adidas said North American sales topped the €1 billion mark for the first time, rising 23% on a currency-neutral basis, a boost that contrasts Nike's 3% fall over the same period to just under $4 billion.
Nike's China's sale grew 9% to $1.108 billion, the company said, but that figure trailed the 28.3% gain for Adidas, which saw total brand sales -- including Adidas and Reebok -- hit €1.102 billion.
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