"As the president said yesterday in the Oval Office to a number of people, he thinks he's doing a great job", she said.
The White House has been rattled by two weeks of muddled messages, departures and spitting matches between the president and his own top officials.
John Bolton: A former USA ambassador to the United Nations who was strongly considered as a candidate for deputy secretary of state during the Trump transition.
Kelly was exasperated by the NBC report because he was only asking about possibilities for McMaster with no timetable, the White House official said.
Aides have discussed for some time an exit strategy for McMaster, who has clashed with Trump on policy matters, including Iran and Afghanistan strategy.
"We frequently face rumor and innuendo about senior administration officials".
Mr McMaster as a solid choice for replacement because he had no ties to the campaign.
Sanders said White House communications director Hope Hicks is leaving to "maybe take a little bit of a break and have some time for herself".
McMaster was not part of Trump's campaign, having joined the White House to replace Michael Flynn, who came under fire and stepped down after admitting that he lied to the Federal Bureau of Investigation regarding conversations he held with then Russian ambassador Sergey Kislyak concerning USA sanctions on Russia and other matters during the transition period following the elections.
The President has privately expressed irritation with McMaster stemming from differences in "personality and style", a senior Republican source previously told CNN. The 29-year-old had been a close friend and former employee of Ivanka Trump, and been considered a close ally of the president before her resignation. Trump's first national security adviser, Michael Flynn, resigned amid controversy over his contact with Russian officials within a month of taking the job.