The Ghanaian midfielder admits the Italians have their work cut out if they are to defeat the defending champions but says Inter, themselves, are in excellent form.
Jose Mourinho's side head into Tuesday's clash unbeaten in six games in all competitions and nine points clear at the top of Serie A.
With that in mind, Muntari believes Inter can beat United in Italy, especially with Mourinho in charge.
Best"United are a great team, one of the best," Muntari told skysports.com.
"But they will find it hard against us because we are also very good.
"They have great forwards but we have our game plan and we have the Jose Mourinho factor, he is the best coach in the world for me."