"Colin, I understand you've filed defamation proceedings against my client. You haven't served them. Pls send immediately," Wilson tweeted.
Craig said he considered suing MacGregor "historically" and also considered taking cases against all of the media organisations that published the content he has alleged is defamatory.
Instead, he said, he decided to take cases against the three people "who fed the media the defamatory information": Conservative Party board member John Stringer, the head of the Taxpayers' Union Jordan Williams and Slater.
Craig believes RNZ has looked at this history, and written their story based on a belief this is something he is considering now - which he is not.
RNZ reported that papers have been lodged, and said Craig said the case would only go ahead if he loses the case now before the court.
He's awaiting a reserved decision after he took blogger Cameron Slater to court over posts made about his relationship with MacGregor.
RNZ said MacGregor was not aware of the latest court action.
High Court spokeswoman Nana Matenga said general proceedings were lodged last year but haven't been served.
"There are no papers on the file to confirm the defendant has been served."
MacGregor resigned two days before the 2014 election and received an out-of-court settlement after making a sexual harrassment complaint against Craig.
She has since been forced to take the stand in two trials the former Conservative party boss has been involved in since his failed political bid.
Craig is involved in at least five court cases involving defamation and copyright issues.
Jordan Williams says he will do everything he can to support MacGregor, should Craig decide to sue her.
He's taken his case against Craig to the Court of Appeal, after the judge who presided over it overturned the decision of a jury to award him 1.27 million dollars in damages for defamation.
"We asked the jury to stop this man destroying people's lives, the jury spoke, and clearly believed Rachel and I. The level of damages is now before the Court of Appeal," he said.
"In my opinion Colin Craig is vexatious and if he does sue Rachel, I'll be doing everything I can to support her emotionally and financially."
