United boss Brian McDermott told the club's official website: "I'm delighted for Ross winning player of the month, quite rightly in my opinion, although I'm biased.
"He's started December well with two goals, and let's hope he can win it this month as well."
Four of McCormack's seven goals came in the 4-2 victory over Charlton at the beginning of the month.
Don Goodman, a Football League pundit for Sky Sports, told leedsunited.com: "McCormack's four goals at Charlton make him the stand out player in the Sky Bet Championship this month and have put him in the hunt for the golden boot.
"The Scotland international is in fine form and Leeds will need to keep him firing for the rest of the season if they are to stay in play-off contention."