Brazil striker Ronaldo is expected to return to training on Thursday despite experiencing dizziness and headaches.
The problems were serious enough for the 29-year-old to visit a clinic for a check-up on Wednesday evening.
A statement on the Brazilian Football Federation's official website explained: "No abnormality was found. Ronaldo is, therefore, in normal conditions for training."
The Real Madrid striker was heavily criticised for his lacklustre showing in the holders' World Cup opener against Croatia and Brazilian fans jeered him as he left the field after being replaced by Robinho.
Despite his ineffective performance in the 1-0 victory, coach Carlos Alberto Parreira has made it clear Ronaldo will start against Australia on Sunday if fit.