All eyes will be on Brazilian star Ronaldo on Sunday. His dismal performance against Croatia during his team's opening match on Tuesday has many scratching their heads with many questioning whether the top goal-scorer from 2002 can be effective in this tournament.

Last week, the Real Madrid star did get some support from Brazilian football idol Pelé, who called for a bit more understanding. "(Ronaldo) left a lot to be desired," said Pelé. "But Brazil needs him and Ronaldo needs our moral support," the footballing legend told German TV channel ZDF. "The time has come to help him. He needs backing now and has to maintain his self confidence."

Brazil's national team trainer Carlos Alberto Parreira, however, was less charitable. "At this World Cup, everyone is fit, plays quickly, covers the pitch tirelessly and switches rapidly between defense and attack. If Ronaldo doesn’t get better, we will have to see what we will do over the course of the tournament." Ronaldo has been confirmed to start in Sunday's game, but the coach insisted he has to improve.

Ronaldo was thoroughly examined on Wednesday night in a Frankfurt clinic after he complained of dizziness and nausea. He underwent an endoscopy, blood tests and several scans, but all test results came back negative. The team's doctor Jose Luiz Runco did not rule out stress as a cause of the latest health problem. Runco said the player was taken to the clinic after feeling unsteady for the second time in less than a week. Although nothing was found wrong, the player was given some medication, including antibiotics.

Ronaldo explained that he underwent the examination as a precaution. "The team is behind me, just as I am behind the team." He said he didn’t ask for any special treatment and expected to play better on Sunday.

The unlucky champion has had a checkered past when it comes to his physical and mental well-being. In the final warm up game before the World Cup, Ronaldo was forced to leave the pitch because of blisters caused by new shoes, a couple of days later he missed practice due to a respiratory infection. There have already been doubts about the superstar's mental toughness. In 1998 just before the final against France, Ronaldo suffered from unexplained convulsions. He did go on to play -- but badly -- and Brazil lost the game 0-3.