President Donald Trump has one word to describe former White House staffer and fellow reality-TV star Omarosa Manigault Newman: "Lowlife."

Ms Manigault Newman claims in an upcoming book, Unhinged, that Mr Trump used racial slurs on the set of his reality show The Apprentice. She also says she later concluded that he is a racist and a bigot.

On Saturday, reporters asked Mr Trump during an event at his golf club in New Jersey if he felt betrayed by Ms Manigault Newman. He responded: "Lowlife. She's a lowlife."

Ms Manigault Newman was a contestant on The Apprentice and later served as a senior adviser to the president. In the book, she paints Mr Trump as scattered, self-absorbed, misogynistic and insecure.

The book is set for publication on Tuesday. The White House has already slammed it as "riddled with lies and false accusations".