CAMPANA, Argentina (AP)

Brazil could be without defender Thiago Silva against Paraguay in the quarter-finals of the Copa America tomorrow night because of a right thigh muscle injury.

Thiago Silva missed Brazil's practice yesterday and doctors said it was unclear whether he would recover in time for the decisive match in La Plata.

Doctors said they will wait to see how the healing process progresses and re-evaluate the AC Milan player today. The Brazilian football federation said the injury stems from natural fatigue after the three group matches.

If Thiago Silva is not able to play, coach Mano Menezes will have to choose between Benfica defender Luisao or Chelsea's David Luiz to play alongside veteran captain Lucio.

The 26-year-old Thiago Silva has been a regular starter since Menezes took over the national team after the World Cup last year. The coach used Thiago Silva and David Luiz in friendlies leading into the Copa America, but then brought Lucio back to add experience to the team, benching David Luiz.

below-average performances

Luisao hasn't played much under Menezes, but he has the experience of having played in the last two Copa Americas, both won by Brazil.

The possible change for Sunday's match could add even more pressure on the Brazilian defence, which has been criticised after below-average performances in the South American competition. Brazil allowed two goals in each of the last two matches after unusual defensive breakdowns and individual errors, including two by goalkeeper Julio Cesar against Ecuador on Wednesday.

"The defence hasn't been playing badly, we just allowed some goals because of mistakes, that happens in football, it's normal," Lucio said.

The coach likely won't have to make any other changes to the team after they improved significantly against Ecuador following the draws against Venezuela and Paraguay in the group stage. Menezes hasn't announced the official line-up, but could leave it unchanged for the first time in the tournament.