The 45-year-old believes that while the Liga leaders can perform without their star man, the Argentine's return to fitness would hand them a huge boost
The Argentine forward has been struggling with a hamstring injury, suffered in the club's quarter-final first leg clash with Paris Saint-Germain, and the club's assistant coach admits he may not feature against the Bundesliga champions.
"There’s no doubt that a player of Leo’s quality has an effect on the way on the way you attack," the 45-year-old said at a press conference on Monday.
"If, unfortunately, he can’t play then [we must remember that] we have won important games without him. But there is no doubt that it is important for Leo to play against Bayern.
"I can’t say for sure how Messi’s going to be tomorrow. We’ll see how he feels today in training, we’ll listen to the doctors and then we’ll decide. If he’s good then we can count on him."
The Blaugrana saw off AC Milan in the last 16 and PSG in the quarter-finals to set up Tuesday's last-four clash with the Bavarians and Roura is expecting a close encounter very different to their recent victories in the competition.
"Every game, every victory is different. This will be a very tight semi-final. It will be won with the small things, the details. We will look to play another extraordinary game like we did at home against Milan," he continued, referring to Barca's second-leg 4-0 win after the 0-2 loss from the first match at San Siro.
"We’re really looking forward to it. It’s a game everybody wants to watch. We’re very happy and we’ll do everything we can to get through.
"It's going to be a party, without a doubt, we are going to play with a high intensity, and the team that is able to impose their system and style will have many advantages.
"We'll try to impose our virtues to control the game. But we know the potential of Bayern."