Nacional goalkeeper Rodrigo Munoz believes he must keep a clean sheet in their match against Estudiantes to reach the final.

The Uruguayans must overcome a 1-0 deficit from the first leg when they meet at the Estadio Centenario in Montevideo tomorrow.

Munoz kept his side in the tie with some key saves in the first leg, including a block to deny Mauro Boselli in a one-on-one situation, but a strike from Diego Galvan means Nacional must recover a deficit on their home turf.

"Keeping a clean sheet is the key. If they do not score, it will be easier for us," Munoz told the Ultimas Noticias newspaper.

"We must remain focused, that will be crucial because any lapse from us, and that includes me, could see us eliminated. That was the reason we lost the first leg.

"Nothing will beat the atmosphere we will live in at the Centenario tomorrow night. We must not miss this chance."

The Centenario promises to provide a daunting venue for the visitors, who will play in front of a partisan crowd following a decision by both clubs to prohibit travelling Argentinian fans from attending the game.

To make matters worse for Estudiantes they will be without playmaker Juan Sebastian Veron due to the leg injury that forced him off at half-time of the first match.

Estudiantes coach Alejandro Sabella, said: "We must face the absence of Sebastian as well as playing as visitors on a very difficult pitch to win. That is made even harder by the decision not to allow our fans to attend.

"This is a crucial test for us, but I trust my players. I have only kind words for them."

In the other last-four tie, Cruzeiro are favoured to progress as they take a 3-1 lead to Gremio.

Cruzeiro could also welcome back Ramires, who helped Brazil to their Confederations Cup success in South Africa this week, but despite their advantageous position the national team star has warned against complacency.

"We should be cautious. Gremio are not an easy team to beat," he said.

"The match will be tough, but Cruzeiro have everything to play for. We have done a good job in the Copa Libertadores and we deserve the title."

Cruzeiro left-back Gerson Magrao also pleaded caution to his team-mates, highlighting the threat of Gremio midfield duo Souza and Tcheco as reason to be wary.

He added: "We must be very careful with Souza. He is very talented and creates the play. Tcheco is also very good from dead-ball situations."

Forward Thiago Ribeiro added: "Dead balls are always worrying, even more in a team that use them like Gremio.

"Small details like this may make the difference so we must be careful."