The WSJ reported that he was sacked over unspecified security issues. According to the Wall Street Journal, McEntee was removed from the White House for an "unspecified security issue". The Washington Post first reported McEntee's firing, and CNN first reported the reason for his firing, citing a source familiar with his firing.
The 27-year-old McEntee was subsequently hired by Trump's campaign as a senior adviser for campaign operations.
Before McEntee was working for Trump, he was a viral star, known for a trick-shot compilation video he released while he was quarterback for the UConn Huskies in 2011.
Trump fired his secretary of state, Rex Tillerson, on Tuesday, and his top economic adviser Gary Cohn resigned last week.
Kelly, the White House chief of staff, has said in recent weeks that too many staff members were operating on interim security clearances because they could not pass Federal Bureau of Investigation background checks.
McEntee, who joined the Trump campaign in its first months, is the latest of the President's longest-serving aides to leave or announce plans to leave the White House, following the resignation of White House communications direct Hope Hicks two weeks earlier.
Mr McEntee, who was most recently seen travelling to Pennsylvania with Mr Trump for a rally on Saturday, was expected to join the president in California on Tuesday before his sacking.
Axios's Jonathan Swan touched on how devastating this will be for morale inside the White House. McEntee's role was described as "body man", always staying by Trump's side.
His exit follows another original Trump campaign aide. "We need the help of proven leaders such as Katrina and John to promote the President's growing portfolio of achievements across the country".