The Knights are courting Brown’s replacement after his shock call to depart the club after four years in charge.
O’Brien and Fitzgibbon are highly regarded around the league and and have reportedly both been internally discussed by the Knights in the past 48 hours.
Kevin Walters is also considered a contender for the job, while the likes of Anthony Griffin, Shane Flanagan, Geoff Toovey, Trent Barrett and Garth Brennan could also be discussed, according to The Sydney Morning Herald.
Brown’s decision to depart the club came as a surprise given Newcastle CEO Philip Gardner’s statement four weeks ago: “Nathan will go down as one of the most important coaches in Knights’ history.
“When he joined our club ahead of the 2016 season, it was at its lowest ebb. The sheer scale of the task he was faced with was monumental. It would have broken a lesser man.
“Put simply, it would be wrong to measure his contribution to the Knights in wins and losses alone. Nathan shaped our roster as he did our club. He once again made Newcastle a place that players wanted to not just play in, but play for.”