They reportedly contacted police in Italy, where Ronaldo lives, playing for Juventus following a $92 million transfer from Real Madrid this summer.
The authorities in Nevada are believed to have found DNA belonging to someone other than Miss Mayorga on the dress she was wearing nine years ago. They want to confirm that it belongs to the footballer.
However, given that he has not denied being in the hotel room with her, and indeed was photographed earlier in the evening in intimate conversation with her, it is not clear what the DNA would prove.
Peter Christiansen, Ronaldo's lawyer, said in a statement issued to The Telegraph: "Mr Ronaldo has always maintained, as he does today, that what occurred in Las Vegas in 2009 was consensual in nature, so it is not surprising that DNA would be present, nor that the police would make this very standard request as part of their investigation."
Mr Christiansen has said that he intends to pursue legal action against German magazine Spiegel, after it interviewed Miss Mayorga and published a detailed account of her accusations in September.
"I felt sick and I felt confused," she told the magazine. "And I still had no emotion. No emotion. Through this whole thing ... it took me three months to cry."
Las Vegas police would not confirm the approach.