United are at the San Siro for the first-leg and Taibi believes tonight's game will be decisive over the tie.
"I think the problem will be Wayne Rooney. He's a complete player, fights, makes goals and defends. Like Milan, however, they have a great team and there are many players who can make a difference like Berbatov and Valencia.
"Without a doubt I am a Milan fan.
"I believe Ronaldinho can decide this tie. He can make the difference."