The bombshell allegations were published in Germany's Der Spiegel magazine over the weekend.
The in-depth article claimed that American woman and former model Kathryn Mayorga, 34, reported the alleged sexual assault at the hands of the Juventus striker to police in 2009.
In 2010, Mayorga was paid US$375,000 to keep quiet about the allegations, according to the report.
Ronaldo took to social media to deny the accusations, calling them “fake news”.
“They want to promote [themselves] by [using] my name. It’s normal,” he said in an Instagram video.
Ronaldo's lawyer, Christian Schertz, also responded to the allegations, slamming the reporting in Spiegel as “blatantly illegal”.
The alleged incident took place in June 2009, when Ronaldo, then 24, was on holiday in Las Vegas and met Mayorga, then 25, in the Rain nightclub at the Palms Casino Resort.
According to the report, the athlete invited Mayorga to a party in his suite, where he then exposed himself to her in a bathroom and forced himself on her while she begged him to stop.
The report added that, “when Cristiano Ronaldo completed the sexual assault of the plaintiff, he allowed her to leave the bedroom stating he was sorry, he was usually a gentleman”.
Mayorga reported the alleged assault to Las Vegas police the next day but then signed a nondisclosure agreement in return for payment.
Der Spiegel said that Mayorga originally agreed to the settlement out of fear and added that she was suffering severe distress and trauma in the wake of the alleged incident.
Ronaldo is suspended from Juventus’ next match against Young Boys in the Champions League this week, and is expected to return to the field during Sunday’s game against Udinese.