And Ronaldinho, also on target in the first leg, says stopping United's top scorer is Milan's priority.
"Rooney was incredible in the first match," said Ronaldinho.
"We have watched videos of the game and the key to victory for us will be stopping him receiving the ball close to our penalty area.
"If we can stop him our own options soar. We can beat United. As far as I am concerned, this match is like the Champions League final itself. I see a very attacking game with many goals."
Milan coach Leonardo also paid tribute to Rooney, claiming the England striker has improved since Cristiano Ronaldo left Old Trafford.
"Rooney is a fixed point of reference in the United team," said the Brazilian.
"It is incredible to see the way he has developed, grown and matured as a player.
"Maybe it has had something to do with Cristiano Ronaldo leaving because it meant he needed to step up."