"I have not resigned but for personal reasons have had to take a step back from the campaign," Murphy said.
Murphy, who joined the Trump Campaign in June, did not specify any reason for this.
He is a close ally of Paul Manafort, Trump's former campaign chairman, having worked together on Bob Dole's 1996 presidential campaign, Politico said. Manafort had resigned from the campaign in August.
Murphy's move comes with just a little over two weeks remaining until the election day. This comes after Trump participated in the last presidential election debate against Democrat Presidential nominee Hillary Clinton on Thursday.
It is unclear though who would be replacing him.