Bayern go into the first-leg in flying form after wrapping up the Bundesliga title in style.
"It is going to be a very tight tie," Roura told reporters as he stood in for Tito Vilanova at the pre-match press conference on Monday.
"It will probably come down to nuances. The side who manages to impose themselves the most on the game will have the best chance.
"We know how good Bayern are, and we know it's going to be hard not only tomorrow, but in the tie overall."