Giuliani, the former mayor of New York City who joined Trump's legal team in April, is preparing Trump by holding in-person and phone sessions with the president, according to the reporter.
The sessions are "to educate me" about what he can say that is not protected by attorney-client privilege, Giuliani also told the reporter.
Giuliani also touched on the alleged use of an FBI informant in Trump's campaign — a revelation Trump has fervently decried as a potential scandal.
Multiple outlets reported that an FBI informant spoke with multiple Trump campaign associates as part of the federal investigation of Russian election meddling. Giuliani told the reporter that he is not yet "satisfied" that the alleged use of an informant was proper, saying he had not seen related FBI documents.
In a Washington Post interview on Tuesday, Giuliani tied the prospects for an interview between Trump and special counsel Robert Mueller's team to the alleged FBI informant.
"We need all the documents before we can decide whether we are going to do an interview," Giuliani told the Post.
Trump has repeatedly claimed that a "spy" was placed in his campaign for "political purposes," an accusation for which no evidence is publicly available.
In remarks to reporters at the White House on Wednesday, Giuliani doubled down on the Sept.1 deadline he had previously floated as the time he expected Mueller to conclude his probe of potential coordination between the Trump campaign and Russia.
"If he doesn't file this report by September 1, mid-September, he's clearly doing a Comey," Giuliani said. He was referring to former FBI Director James Comey, who made statements about an investigation into former candidate Hillary Clinton's email server shortly before the 2016 election.
He added that Democrats "want to see the investigation stretch out past the next midterm elections," despite recent statements to the contrary from some Democrats.
The White House did not immediately respond to CNBC's request for comment.
Clarification: This story was updated to reflect additional comments and context from Giuliani.