Pictures showed Ronaldo being struck as he was escorted off and one showed him with a badly bruised and swollen right eye. Following the incident, he left the stadium without talking to the media.
"He had a good debut, moved well and tried a few dribbles," Corinthians coach Mano Menezes told reporters.
Last February, Ronaldo ruptured a tendon in his left knee in a Serie A game playing for AC Milan against Livorno and later left the Italian club.
He joined Corinthians in December in a surprise move and has taken nearly three months to reach match fitness.
Ronaldo was involved in another off-field controversy last week when he was fined by the club for arriving late at the team hotel after a day off.
Corinthians were already 2-0 ahead when Ronaldo came on, Chicao and Andre Santos having scored either side of halftime.
Wearing his favourite number nine shirt, Ronaldo had only a few touches of the ball in an unspectacular debut. It was his first game for a Brazilian club since leaving Cruzeiro in 1994.
The former Barcelona, Real Madrid, PSV Eindhoven and Inter Milan player had previously suffered two serious injuries to his other knee and many observers speculated that he would not recover from the latest setback.
Even before the latest injury, he had been suffering from a loss of form and weight problems and had not played for Brazil since his much-criticised performance at the 2006 World Cup. (Reporting by Tatiana Ramil; Writing by Brian Homewood; Editing by John O'Brien)
