"What you saw the other day was as serious as it can get. This is a direct attack on the institutions," Bannon said during a flying visit to Italy. "This is a coup, okay".
Bannon who worked with him first as his campaign manager and then as his chief strategist at the White House was fired by him last August.
Bannon was quoted in a new book about the Trump White House as calling Donald Trump Jr. "treasonous" and "unpatriotic" for meeting during the 2016 presidential campaign with a Russian lawyer who was said to have damaging information on Democratic candidate Hillary Clinton.
"The President has been very clear on his thoughts; issued a four-paragraph statement about Mr Bannon. Zero ambiguity in those statements. It was obvious that the book was false and fake," Gidley said.
Bannon, 64, was the top manager of the Trump campaign and the White House chief strategist in the first seven months of the Trump administration. He was fired on August 18.
Bannon damaged his standing by giving an interview to the liberal American Prospect this week in which he was seen to be undercutting Trump's position on North Korea.
Notably, the statement comes a day after US President Donald Trump's chief strategist Steve Bannon said there was no military solution to the threat posed by North Korea and its nuclear ambitions, despite the president's recent pledge to answer further aggression with "fire and fury."
President Donald Trump has removed chief strategist Steve Bannon from the National Security Council, reversing a controversial early decision to give Bannon access to the high-level meetings.