The running back lost the ball in his first game since breaking his leg last November, which the Giants won 18-13.
The head coach told reporters: "His eyes never went to the ball. He never looked at the ball. He was looking at the rush and fumbled the ball. By the time he got to where he started looking for the ball, the defenders were on him."
Brown added: "I know I can be in the doghouse when you fumble the ball, especially with coach Coughlin. I know he's going to be on me this week about holding onto the ball and my protection."
Brown rushed for 23 yards from four carries during the game.