"There's every possibility the special counsel is looking at some process-related crime that doesn't relate to Russia," Stone told CNN's Anderson Cooper on Friday night.

"I obviously believe the special counsel has a political bias, as demonstrated by the FBI text messages and emails that have surfaced and the political nature of this investigation, so I think it is very dangerous for the President to do so," Stone, a longtime Trump confidant, added.

Stone's message to Trump comes in response to a CNN report on Friday that the President began initial steps to prepare for a possible interview with the special counsel, according to a White House official and a person familiar with the situation.

One source familiar with the proceedings stressed that the preparation effort is "in its infancy." The preparations have been short and informal and have included going over potential topics with the President that Mueller would likely raise in an interview, the people said. The President has not formally agreed to sit for an interview with Mueller.

Mueller is leading the special counsel's investigation into Russian meddling in the 2016 election, and the probe is examining any potential ties between Russia and Trump campaign associates. The President has repeatedly denied any collusion.

Although critical of the special counsel investigation, Trump has been publicly receptive to the idea of sitting down with Mueller.

On Tuesday, The Washington Post reported Mueller had told Trump's lawyers that the President is not currently considered a criminal target of the Russia probe, citing three people familiar with the discussions.

The Post's report also noted that Mueller continues to seek an interview with Trump. CNN reported last week that attorneys for both sides sat down for an in-person meeting on topics that investigators could ask the President about, according to two sources familiar with the talks.

However, last month, Trump lawyer John Dowd resigned from the President's personal legal team over disagreements regarding the handling of the Russia investigation.
Stone said he agreed with Dowd: "I think Mr. Dowd, who I read had advised against this, was correct," he said, referring to the President sitting down with Mueller.

More about: Trump