BUENOS AIRES, Oct. 22 (Xinhua) -- Gremio defender Walter Kannemann admitted on Monday that he is unsure how to beat River Plate as the teams prepare for Tuesday's Copa Libertadores semifinal first leg here.

River have conceded just two goals from their past eight Copa Libertadores matches and just four in total in the current edition of South American football's top club competition.

When asked by a reporter how the defending champions plan to overcome the Argentine giants in Tuesday's match at the Monumental stadium, Kannemann replied: "If you have that information, please tell me."

"It's going to be a game in which we have to concentrate and can't afford to give anything away. We will focus on getting through the early stages and then try to win the match."

The 27-year-old center-back added: "We're ready for everything. River are renowned for their intensity and pressing so it's going to be a difficult game. But anything can happen, even against a strong rival like River Plate."

Mystery continues to surround the availability of Gremio talisman Luan, who made the trip to Buenos Aires despite a foot injury. Kannemann gave no clue about whether last year's Copa Libertadores player of the tournament would be fit for the match.

"We don't know if he is going to play," Kannemann said. "If he is on the pitch it will be a big plus but we are still a strong team without him," he added.