Juventus president Andrea Agnelli says he will support Cristiano Ronaldo as the forward faces a rape allegation.

American Kathryn Mayorga has accused Ronaldo of sexually assaulting her in a hotel in Las Vegas in 2009, something the Portuguese has strenuously refuted.

German publication Der Spiegel first reported the claims, which also included the suggestion Ronaldo paid Ms Mayorga $375,000 in 2010 as part of a privacy agreement, preventing her from going public with the allegations.

Ms Mayorga filed a lawsuit in an attempt to quash that agreement while Las Vegas police have re-opened an investigation.

Ronaldo's lawyer Peter Christiansen confirmed the payment was made to Ms Mayorga, but said some documents presented as evidence had been "stolen" and "completely fabricated".

In a statement released earlier this month, Ronaldo described rape as an "abominable crime" and Agnelli confirmed at a news conference on Thursday he will back the player.

"When there are problems I tend to look people in the eyes, ask them the questions directly and them judge them myself," Agnelli said at a news conference. 

"I'm very calm, having spoken to him directly as soon as the case emerged, on his position. And his behaviour in the days and weeks that followed only confirm my initial feeling.

"It's a personal case, but I spoke to him with [vice chairman] Pavel [Nedved] and [sporting director] Fabio [Paratici] and I told Cristiano that my door and the door of Juventus will always be open whenever he would need something.

"We are here to support him and the same goes for every woman and man at Juventus, when they need it and when we are convinced that they behaved correctly."

Ronaldo addressed the allegation when he appeared at a news conference ahead of his return to former club Manchester United for a Champions League fixture this week.

"I am a happy man," he told reporters. "We did the statement two weeks ago, if I'm not wrong. I am glad, of course, I'm not going to lie in this situation, I'm very happy. 

"My lawyers, they are confident and of course I am, too.  The most important thing is I enjoy the football, I enjoy my life.

"The rest, I have people who take care of my life. Of course, the truth is always coming in the first position. So, I'm good."