McCormack is the Championship's top scorer this season with 17 goals in 26 appearances and his displays have attracted the interest of Sam Allardyce.
The West Ham manager has seen his attacking options limited by injuries during the first half of the Premier League campaign, prompting reported interest in a number of strikers in the January transfer window.
Scotland international McCormack was the latest player to be linked with the Upton Park club and Leeds have now confirmed a bid has been turned down.
"We received an offer from West Ham this afternoon (Friday) for Ross, which we have rejected," managing director David Haigh told the club's official website.
"As a club we showed our intentions as far as Ross is concerned during the summer by offering him a new contract."
Leeds have lost their four Championship matches and sit 12th in the table.
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