Washington (CNN) White House national security adviser Lt. Gen. H.R. McMaster could leave his position in the White House by the end of the month, according to an administration official.

Multiple sources familiar with the matter have said McMaster's departure is likely in the near future.

The administration official and a source familiar with the matter say it is becoming more likely that McMaster will not return to the military and ultimately will retire as a three-star general.

Among the names being considered to replace him are:

Safra Catz: CEO of Oracle and a former member of the Trump transition team.

John Bolton: A former US ambassador to the United Nations who was strongly considered as a candidate for deputy secretary of state during the Trump transition. Bolton has maintained what some have described as a positive personal relationship with President Donald Trump since the election but his hawkish views on issues like North Korea have made him a controversial pick to join the administration.

Sources caution that Trump will make the final decision and things could always change.

Two sources with knowledge of the matter said McMaster has talked to senior leadership at the Hoover Institution about a position there once he finishes at the White House. But another source emphasized that "no deal or arrangement has been finalized."

National Security Council spokesman Michael Anton dismissed reports of McMaster's departure, telling CNN, "I was just with President Trump and H.R. McMaster in the Oval Office. President Trump said that the NBC News story is 'fake news,' and told McMaster that he is doing a great job."

Secretary of Defense James Mattis' office referred all questions regarding personnel matters to the White House.

At least one senior military officer has been informally approached about whether he would be interested in the national security adviser job and has said no because of the officer's belief that he could not fill what's essentially a political job while serving in uniform, according to an official familiar with the situation.

Aides have discussed for some time an exit strategy for McMaster, who has clashed with Trump on policy matters, including Iran and Afghanistan strategy. While chatter of McMaster's departure has persisted for months, there now appears to be a scaled-up effort to locate a replacement.

White House principal deputy press secretary Raj Shah denied that any departure is imminent: "We frequently face rumor and innuendo about senior administration officials. There are no personnel announcements at this time."

Last week, CNN reported that McMaster could leave the White House after months of tensions with Trump.

The President has privately expressed irritation with McMaster stemming from differences in "personality and style," a senior Republican source previously told CNN.

The two have never gotten along, and Trump continues to chafe at McMaster's demeanor when he briefs him, feeling that he is gruff and condescending, according to a source who is familiar with his thinking.

But the task of easing McMaster out of his role as national security adviser presents a unique challenge for the White House.

Sources with knowledge of McMaster's standing in the White House have repeatedly said that he has been on thin ice for months.

There was discussion in the West Wing about replacing him last fall, but he ultimately survived because officials, including the President himself, were skeptical about the optics of appointing a third national security adviser in less than a year, several sources told CNN. Trump's first national security adviser, Michael Flynn, resigned amid controversy over his contact with Russian officials within a month of taking the job.

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 Russia investigation, according to a senior Republican source.