The Real Madrid star, who completed him move to the Bernabeu today, reportedly kicked in the window of the car on the side that the girl was sat on, leaving shards of glass all over her.
It is alleged that he leapt out of his £200,000 red Ferrari 599 GTB Fiorano to confront the girl.
The reports go on to suggest the teenager was treated in hospital for cuts on her arm, before reporting the attack to police.
While Pardal is said to have claimed she was simply a fan of the Portugal star, some reports suggest she was either a freelance paparazzi photographer, or was accompanied by a photographer.
The Sun newspaper quotes Ronaldo apologising for the incident, which occurred in Lisbon on Sunday: "I was accompanied by my mother, and he by a young woman who throughout our whole journey ostensibly and provocatively filmed all our movements.
"This persecution caused my mother to be so disturbed and upset that I had to stop my car to try to convince them to leave us in peace.
"I try to swallow it and remain indifferent. But when my mother is involved, then I'm sorry but I don't let anyone, I repeat anyone, harass her.
"I regret what I did, but I can't promise that I would not react in the same way again in the same circumstances."
Ronaldo's management company released a statement which said: "Because of his mother Dolores' despair, Cristiano Ronaldo finally reacted impulsively, kicking the car of the individual concerned and his travelling companion."