A former American model, Kathryn Mayorga, 34, of Las Vegas, accused Ronaldo in a complaint filed a year ago in Nevada of raping her on Jun 13, 2009 just before he joined Real Madrid from Manchester United.
Lennard claimed that she was told by Ronaldo that, if she were to date anyone else or even leave her house, he would have her "kidnapped and have [her] body cut up and put in a big and thrown into a river".
Ronaldo has not been served with the lawsuit, Mr Christiansen said.
The warrant has been sent to authorities in Italy, where Ronaldo now lives.
Las Vegas police recently requested a DNA sample from Cristiano Ronaldo as part of an ongoing investigation into an alleged 2009 rape, reports the Wall Street Journal's Zusha Elinson, citing a law-enforcement official with knowledge of the situation.
The reports state that the warrant has been sent to the court system in Italy, where the five-time Ballon d'Or victor plays for league leaders Juventus.
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The lawsuit is on and the criminal police investigation are on separate legal tracks.
Ronaldo and his lawyers repeatedly denied the claims when they first emerged in October, and at one point his lawyers threatened to sue the German news magazine that was the first to publish Mayorga's accusations. The suit states Ronaldo apologized "stating he was sorry, he was usually a gentleman". Lennard has since been in contact with Mayorga's team and will be looking to share her evidence with them.
She said she wanted the agreement to be declared void, explaining that she had gained the courage to speak out because of the #MeToo movement. The Journal reported that Mayorga's DNA is on the dress, and so is the DNA of an unknown party.
But the investigation ended a short time later because Las Vegas police say she only identified her attacker as a European soccer player - not by name - and did not say where the incident took place.
Ms Mayorga reported the alleged sexual assault to police on the day it occurred.