Kristin Davis, the "Manhattan Madam" who says she provided prostitutes to New York's rich and famous, is scheduled to testify before special counsel Robert Mueller's grand jury in Washington this week, according to a person with knowledge of the matter.

Last week an investigator on Mueller’s team questioned Davis about Russian collusion, said the source.

Davis declined to comment. Her lawyer could not immediately be reached for comment.

Davis, 41, told NBC News in July that someone in Mueller's office called her attorney to ask her to speak to investigators, and that she believed it was because of her ties to former Donald Trump adviser Roger Stone. She also said she had no knowledge of Russian collusion.

A spokesman for Mueller's office declined to comment.

In a statement to NBC News last week, Stone said: "Kristin Davis is a long-time friend and associate of mine. She is a brilliant businesswoman who paid her debt to society and remade her life. … She knows nothing about alleged Russian collusion, WikiLeaks collaboration or any other impropriety related to the 2016 election which I thought was the subject of this probe. … I am highly confident she will testify truthfully if called upon to do so."

Davis said in July that the Mueller representative who contacted her lawyer asked if she would accept a subpoena or if the FBI would need to serve it to her. She said her lawyer called the representative back to say she would accept it.

Davis said at the time she didn't have any information about why she was contacted. Her then-attorney Daniel Hochheiser did not respond to a request for comment.

"It's very out-of-the blue for me, very upsetting," Davis said. "For them to come to me for information on Russian collusion — I don't have anything on that."

However, Davis said, she had worked for Stone for many years, and other people who worked with Stone had already been subpoenaed.

"I’ve been with Roger since 2010 doing web design and writing position papers," she said.

Davis said she couldn't have worked on Trump's presidential campaign and has no information about it because she was in prison during much of that time.

She 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.

Davis had previously spent several months in New York's Rikers Island jail for procuring prostitution. She earned the nickname the "Manhattan Madam" in New York's tabloids after saying publicly that her escort service had about 10,000 well-heeled clients. She said Eliot Spitzer, New York's governor at the time, had been among her clients.