"After he told us he felt dizzy, which had already happened, we decided to investigate," Runco said.

The player underwent an endoscopy, blood tests and several scans, Runco said, adding all results came back negative.

Runco also said he could not rule out stress as the cause of Ronaldo's latest problem.

"I felt sick on my day off and the doctor took me to the hospital for a series of examinations," Ronaldo said Thursday. "There was nothing abnormal and it gave us the peace of mind we needed. I'm feeling much better today."

He went through a stretching session at the team's base outside Frankfurt and was put through some running drills in the afternoon.

He wasn't making any excuses for his poor showing against Croatia.

"I'm aware that it wasn't the performance I would've liked for the opener," Ronaldo said. "But the important thing was that we won the match, now it's try to improve to get better for the next match."

Still, he could find himself benched again if he doesn't improve _ Brazil isn't exactly lacking for scoring threats to replace him.

Ronaldo was with Brazil when it won the title in 1994 and 2002, and he could join Pele as the only player on three World Cup-winning squads. Pele played on Brazil's teams in 1958, 1962 and 1970.

Ronaldo came close to a third title in 1998, but he had unexplained convulsions in the hours leading up to the final. He played poorly, and Brazil lost 3-0 to host France.