WASHINGTON — Attorneys for Andrew Miller, a former aide of ex-Trump adviser Roger Stone, said that Miller has been held in contempt of court for refusing to appear in front of the grand jury hearing testimony in special counsel Robert Mueller's Russia probe, his lawyers said Friday.

Miller had earlier fought to quash a subpoena from the special counsel's office but was ordered to appear Friday morning. He did not, said his lawyer Paul Kamenar outside U.S. District Court in Washington, and was "held in contempt, which we asked him to be in order for us to appeal the judge’s decision to the court of appeals."

His lawyers are challenging the legitimacy of the special counsel and how he was appointed. The U.S. District Court rejected the argument, and his lawyers are appealing.

"Mr. Miller intends to appeal the Court’s July 31 decision regarding the appointment of Mr. Mueller," Alicia Dearn, one of Miller's attorneys, told NBC News. "That is the current posture of the case."

Dearn declined to comment on what duties Miller performed for Stone during 2016. "We cannot respond to these questions due to secrecy rules related to grand jury proceedings," said Dearn.

Another Stone associate, Kristin Davis, is set to testify before the grand jury Friday afternoon.

"[I’m] feeling good," said Davis Thursday. "Not worried at all. Ready for it to be over and moving on with my life."

Davis, known as the Manhattan Madam for providing prostitutes to New York's elite, was in prison on an unrelated charge until May 2016, and said she would not know much about the Trump campaign.

"I didn't work for Roger in 2016," Davis told NBC News Thursday. "I still don't know the scope of what they're going to ask me."

Davis said that Miller was in charge of maintaining Stone's schedule during the presidential campaign. She said she took over that task in August 2017. Davis, 41, has done web design and office tasks for Stone's political consultancy.

Davis told NBC News in July that someone in Mueller's office called her attorney to ask her to speak to investigators. A member of Mueller's team interviewed her last week, said a person with knowledge of the matter.

Davis's lawyer, Miller and a spokesman for Mueller's office did not immediately respond to requests for comment.

In a statement to NBC News, Stone said: "Kristin Davis has been a friend and has worked on and off for me. She is a brilliant business woman who paid her debt to society and has remade her life. She is a single parent of a 2-year-old son who is my godson, Carter Stone Davis, who my wife and I love very much."

"She is most certainly not involved in any illegal activity today and is not seeking a media circus surrounding her testimony while she tries to raise a child and launch a cosmetology business in New York. Kristin Davis was not working for me in either 2015 or 2016 — during the preparation and conduct of Donald Trump’s campaign."

Davis was arrested in 2013 after allegedly selling drugs to an FBI cooperating witness. She pleaded guilty to a charge of selling prescription drugs. Sentenced to two years in prison, she was released in May 2016.