MONTERREY: Copa Libertadores scrambles to return to normal this week after Mexican clubs San Luis and Chivas Guadalajara withdrew due to the swine flu outbreak and two South American teams refused to play in Mexico.

Brazilian club Sao Paulo, which was to play Chivas in the home-and-away series, and Nacional of Uruguay, the opponents of San Luis, now get byes to the quarterfinals.

Despite the chaos, there will be five second-leg matches and one first-leg game this week.

Boca Juniors playmaker Juan Roman Riquelme is set to make his return from injury in the Argentine club's clash with Uruguayan side Defensor Sporting on Thursday. Defensor was scheduled to host Boca in the first leg last week, but the game was postponed because the stadium in Montevideo was unavailable.

The delay gave Riquelme, Boca's key player, extra time to recover from a foot injury, and he seems ready.

"This is where the cup begins for real and I want to play," Riquelme said on Fox Sports in Argentina. "One mistake and you are out." Return legs will be played in five other final-16 fixtures this week. The the first legs were: Sport Recife 1, Palmeiras 0; Caracas 1, Deportivo Cuenca 2; Gremio 3, Universidad 0; Cruzeiro 2, Universidad de Chile 1; and Libertad 0, Estudiantes 3.

Organizers are hoping this week's matches will overshadow the nasty dispute last week between the Mexican Football Federation and CONMEBOL, the governing body of South American football. Last week, the Mexicans not only dropped out of the Copa Libertadores, but said they would not participate in two other continental championships.

Mexican clubs are part of the North and Central American federation (CONCACAF), but have received an invitation to play in the Copa Libertadores every year since 1998.

Mexican clubs have also played in the Copa Sudamericana and the Mexican national side regularly competes in the Copa America, the South American continental championship. Both are CONMEBOL competitions.

The decision to withdraw from the Copa Libertadores was seen - in Mexico at least - as one forced on Mexican officials. This quickly stirred resentment with one Mexican club official saying the South Americans' refusal to visit bordered on "racism."