"I was hit by two microphones and knocked by a camera on the forehead," he told a news conference. "It's difficult for me because I've only really played in Europe and there the organisation is different."
Ronaldo, who suffered a serious knee injury in February last year, made his debut for Corinthians and played his first competitive game for 13 months when he came on as a second-half substitute in the 2-0 win away to modest Itumbiara in the Copa Brasil.
As soon as the final whistle went, he was surrounded by around two dozen reporters and cameramen who rushed onto the field and suffered a swollen eye after being hit my one of the microphones.
"When the game finished, I saw a load of people running towards me... Fortunately, the security men arrived. I'm not used to it and I was frightened.
"When I'm on the pitch, I'm concentrating on the game. I can't answer questions when I'm warming up," he said.
Ronaldo began his career with Brazilian club Cruzeiro but left at the age of 17 to join PSV Eindhoven. He has since played for Barcelona, Inter Milan, Real Madrid and AC Milan.
Media scrums are common at Brazilian games where radio and television reporters are allowed to stand on the touchline or behind the goals and often attempt to interview players who have just scored a goal or have been sent off.
Ronaldo added: "I'm happy to have played my first game, it removes a bit of the pressure. But I need to lose a little more weight so that I can be faster and decisive."
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