The Clark County District Attorney's Office said it had declined to prosecute the Portuguese star because it "cannot be proven beyond a reasonable doubt" that a sexual assault occurred.
Kathryn Mayorga, a former model, has claimed that Ronaldo raped her in a Las Vegas hotel in 2009.
The former Manchester United and Real Madrid star reached a financial settlement with her following the incident but has denied allegations of sexual assault.
The district attorney's office said it had received a report from Mayorga – who it identified only as "V" – on June 13, 2009, reporting that she had been the victim of a sexual assault.
Police were unable to conduct an investigation at the time because she declined to say who assaulted her or where it occurred, the office said in a statement, but Mayorga contacted police in August of last year to ask that the case be reopened, at which point she named Ronaldo as the alleged assailant.
"Based upon a review of the information presented at this time, the allegations of sexual assault against Cristiano Ronaldo cannot be proven beyond a reasonable doubt," prosecutors said. "TherefRead More