The Catalan giants travel to San Siro to face the Italians in their last-16 clash and Roura, who is filling in for Tito Vilanova during his recovery from cancer, believes that his side do not have the advantage.
"You cannot talk about favourites in a tie like this," Roura told reporters.
"Milan are a great team and it is not easy to play against them. The qualification will be decided in Barcelona [in the second leg].
"In recent games we have been conceding goals, but fortunately we always scored a few more. We have tried to resolve certain situations in defence, as you can't always fight back to win."
The second leg of the tie will be played on March 12 at Camp Nou.