Knight was sent off when he was adjudged to have denied an obvious goal-scoring opportunity by fouling Michael Ballack in first-half stoppage time of the 4-4 draw.
He now faces a one-match ban and will miss Saturday's game against Wigan.
Speaking after the FA's decision, Villa boss Martin O'Neill told Sky Sports News: "I'm disappointed obviously otherwise we wouldn't have done it in the first place but I can understand the situation.
"The referee has a decision to make at the end of the day and I understand that he needs some sort of support from the powers that be otherwise there would be absolute chaos.
"I'm disappointed because I thought that we had a case but I accept the view point that the referee in the course of the game has given an honest assessment of the situation."