Speaking to reporters on Air Force One, Trump said he "didn't make that decision - it was made by a man who's a very respected person, a very, very respected person".
Previously, the president has blasted AT&T and Time Warner's merger plans - and during the 2016 election he threatened to block the companies from combining under his watch.
United States authorities have told AT&T and Time Warner they must sell the CNN news channel or satellite operator DirecTV to get the green light for their merger, a source close to the deal told AFP on Wednesday.
According to the Post, the president was likely referring to the Justice Department's newly confirmed antitrust chief Makan Delrahim, who is overseeing the AT&T transaction - and who supported Trump in the campaign and served as a White House lawyer.
Reports conflicted this week about whether AT&T and Time Warner are being asked to sell CNN as part of the merger, in order to avoid monopoly regulations.
This week, Delrahim and other agency officials told AT&T that the deal as it now stands raises anti-competition concerns, and that the company will need to shed some assets, perhaps either Turner or DirecTV. Then he added: "I do feel you should have as many news outlets as you can - especially since so many are fake". The Department of Justice said it does not comment on pending investigations, but that it was "committed to carrying out its duties in accordance with the laws and the facts".
Monday, the DOJ advised the companies that it would not sign off on the merger unless they agree to divest the merged company of CNN, which the president regularly condemns as a supposed purveyor of what he calls "fake news".
"I did make a comment in the past as to what I think", Trump said. The source said the companies were told that Time Warner would need to sell off Turner, the television division that includes CNN.
Raj Shah, a White House spokesman, said in a separate statement that Trump "did not speak with the Attorney General about this matter, and no White House official was authorized speak with the Department of Justice on this matter". The Justice official said no decision on the deal has been reached yet and that conversations continue.