Barca welcome the Italian giants to Camp Nou, with the Rossoneri in pole position to reach the quarter-finals after a 2-0 win in the first leg.
"We're very excited to play the match and we're eager to compete," Roura, who is in charge while Tito Vilanova undergoes cancer treatment, told the club's website after yesterday's league win over Deportivo La Coruna.
"We will give everything we have to fight back until the referee blows the final whistle.
"Logically, we have to attack. However, we shouldn't confuse our desire to fight back with haste, we need to find the necessary balance."
A Milan goal at Camp Nou will require Barca to score four because of the away goals rule.