Villa host United having beaten Bayern Munich in the Champions League in midweek.
Emery said: "I told the players I prepared more for Ipswich than Bayern Munich.
"Why? Because I knew before how we were more or less motivated and excited to face Bayern. We could lose, draw or win but the response of the players I knew before was going to be a high level and we did.
"But against Ipswich I had my doubts if they would respond with the same motivation and mentality. On Sunday against Manchester United, it is always a tough match and matches like that are matches which are very motivating for the players, supporters and myself.
"The Premier League is the best in the world because you are facing in Europe a team like Bayern Munich on Wednesday and then a team like Manchester United in our league. Tottenham, Liverpool, Manchester City, they are huge matches for the supporters, coaches and players."