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Sao Paulo and Nacional of Uruguay stand in the way of the respective Mexican sides and a spot in the quarterfinal round of Copa Liberatdores.

Guadalajara and San Luis learned their opponents for Copa Libertadores' Round of 16 stage on Thursday as tournament organizers scramble to find a place to play the first legs.

Guadalajara will play a familiar side in Brazilian club Sao Paulo while San Luis will meet Uruguayan side Nacional.

Where - or even if - the first legs will be played remains another matter altogether. Mexico is seemingly not an option due to the swine flu outbreak that has reportedly claimed more than 150 lives in Mexico and is nearing a pandemic stage across the globe. The Mexican Football Federation and CONMEBOL had apparently reached an agreement to play the games in Colombia but the Colombian government said no.

If the games do take place, Chivas will meet up against a familiar opponent in Sao Paulo. Chivas and Sao Paulo played a series in the 2006 Copa Libertadores tournament as the two teams met in a semifinal. Sao Paulo denied Chivas the opportunity to reach the final and instead reached the final and won the tournament. Sao Paulo finished with a 4-1-1 mark in Group 4.

Nacional, meanwhile, will be San Luis' first-ever Libertadores knockout round rival. San Luis reached the Round of 16 in their first-ever Libretadores tournament in dramatic fashion as they beat Libertad 2-0 and went to the knockout round after Universitario lost to San Lorenzo 2-0.

For San Luis, Nacional will pose a challenge. Nacional meanwhile won Group 5 with a 4-0-2 record and were one of two teams not to have lost during the tournament's group stage.