'The allegations of sexual assault against Cristiano Ronaldo can not be proven beyond a reasonable doubt, ' they said in a statement.
A district attorney in the state of Nevada said it would not prosecute the Portuguese soccer player because it "cannot be proven beyond a reasonable doubt" that a sexual assault occurred.
However, prosecutors said on Monday they could not substantiate Mayorga's claims, and therefore "no charges will be forthcoming." .
Her lawsuit says she met Ronaldo at a nightclub and went with him and other people to his suite at the Palms Hotel and Casino, where he assaulted her in a bedroom.
The woman and Ronaldo, through their respective attorneys, eventually reached a civil settlement related to this matter in 2010.
Her attorneys say Mayorga never wanted her name released but became anxious that she would be identified after a 2017 media report apparently referred to the encounter.
Ms Mayorga says he pulled her onto a bed and tried to have sex with her as she fought him off, only for him to rape her she screamed "no, no, no".
Neither Ronaldo's nor Mayorga's lawyers responded to AFP's request for comment on the decision to end the investigation. She has a lawsuit pending against Ronaldo in USA court in Las Vegas. A judge has given them an October 28 deadline.
Since the woman did not give any more information a meaningful investigation wasn't conducted. In addition, video evidence, showing interactions between the victim and perpetrator before and after the alleged crime, was lost.
The accuser filed a police report describing the alleged attack, but did not name Ronaldo in the original document.
"On August 28, 2018, V contacted the Las Vegas Metropolitan Police Department, asking that her sexua assault investigation be reopened, naming Cristiano Ronaldo as the offender".