Special counsel Robert Mueller hasn't decided whether to investigate President Trump as part of the Russia probe, according to a report on Sunday.

"Now, my sources are telling me he's begun some preliminary planning," Pierre Thomas, the ABC News senior justice correspondent, said of Mueller on ABC's "This Week." "Plans to talk to some people in the administration. But he's not yet made that momentous decision to go for a full-scale investigation."

Last week, the Washington Post reported Mueller is investigating the president for obstruction of justice in light of his firing of former FBI Director James Comey, something the president's legal team is denying.

"Now Mueller faces a huge decision," Thomas said. "Does he believe the president, who says there's no wrongdoing here, or does he go after the president in the way James Comey wants him to do?"

On Friday, Trump responded to the Washington Post story by tweeting: "I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt."

But attorney Jay Sekulow, a member of Trump's legal team, insisted Sunday the president was not literally confirming the investigation but was just referring to the story.

"Let me be clear: the president is not under investigation as James Comey stated in his testimony, that the president was not the target of investigation on three different occasions," Sekulow said Sunday. "The president is not a subject or target of an investigation."