Although the White House denied the NBC report, strains in relations between the advisor and the president had been widely reported on previously.
National Security Adviser H.R. McMaster last month.
Since then, McMaster has publicly clashed with President Trump on the Russian Federation investigation and his relationship with the president has reportedly gotten tense.
He chose to remain an active duty Army Lieutenant General instead of retiring from military service when he was appointed as National Security Adviser.
McMaster also kept his job at the time because of the White House's challenge attracting top talent for positions in the administration, due to Trump's "blacklist" of individuals who have criticized him, his personality and the Russian Federation investigation, according to a senior Republican source.
McMaster griped that Mattis, a former four-star Marine Corps general, treated him "like a three-star" as opposed to an equal in the administration, according to The Post.
A National Security Council spokesperson dismissed the reports, saying Trump called the story "fake news" and said McMaster is doing a great job.
NBC reported Thursday that Ford Motor Company Vice President of International Affairs Stephen Biegun is one likely successor to McMaster.
"I was just with President Trump and H.R. McMaster in the Oval Office", Anton said Thursday evening.
Despite the denials, White House sources tell Fox News that there are many people in the West Wing - including Trump himself - who would rather see McMaster removed from his position. He is perhaps best known for his PhD dissertation which later became the best-selling book "Dereliction of Duty".