Promising Brazil star Lucas said he "witnessed a lamentable scene" when he tried to give his jersey to the girl after Sao Paulo's match against Coritiba on Sunday. He said other Coritiba fans "tried to attack the girl and her father" because she asked for the shirt.
In Sao Paulo, fans of Corinthians threatened the Scottish tourist because of his green and white Celtic jersey, the colours of city rival Palmeiras, and forced him to hide it before police had to intervene.
Lucas, who has a huge fan base among youngsters in Brazil, said he was trying to give the girl a gift after she supported him and yelled his name the entire match at Couto Pereira stadium in Curitiba.
"I was very scared at the time, a lot of people gathered around them and forced her to give the jersey back," Lucas said.
Television images showed dozens of police officers taking the girl and her father away as fans yelled at them, pointing fingers and making threats.
"I know I was a bit naive, but I never thought that the other fans would have had that attitude, especially with a girl. It was really very sad," the player later said on Twitter.
Lucas, who will join Paris Saint-Germain at the end of the year, said that he was "relieved" that nothing happened to the girl and her father.
Local media said the girl, named Milena and likely in her early teens, was later taken to Sao Paulo's changing room and met with Lucas, who finally gave her his jersey.
"We need to make sure our country is worthy of hosting a World Cup and show that we are civilized," Lucas said.
Incidents between organized groups remain the biggest cause of fan violence in Brazil, which will host the 2014 World Cup and next year's Confederations Cup.
Football rivalry often turns violent, although there have been few serious incidents reported recently. Local authorities in the past used to advise fans not to wear their team's jerseys on the streets near stadiums where opposing clubs played. There were many reports of attacks against random fans just because they were wearing rival jerseys.
In Sao Paulo, fans of defending champion Corinthians grew agitated at Pacaembu stadium because of the Scottish tourist's green and white Celtic jersey.
The fans, seating in one of the stadium's most expensive sections, wanted him to remove the jersey and threatened to do it by force if he didn't comply. The tourist apparently didn't understand what was happening, according to ESPN Brasil, and police had to intervene.
They took the tourist away and he was sent to a different seating section, but only after covering the Celtic jersey with a sweater.
Follow Tales Azzoni at http://twitter.com/tazzoni