Washington (CNN) Roger Stone is warning that President Donald Trump could get caught in a "perjury trap" if he sits down with special counsel Robert Mueller.

"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.

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