Now it appears Sione Mata'utia may have played his last game in the blue and red, at the age of 24.

The powerful back-rower, who in 2014 became the youngest-ever Kangaroo, is contracted to the Knights for next season but has been weighing up a three-year deal to join Super League champions St Helens.

Knights chief executive Phil Gardner declined to comment on Friday about what he labelled "speculation" surrounding Mata'utia's future.

Newcastle coach Adam O'Brien said nothing was finalised yet.

"We'll just sit down at some stage and discuss what is best for Sione and best for the club," he said.

St Helens are coached by Kristian Woolf, who was an assistant at the Knights last season and eventually assumed the head role for three games after the departure of Nathan Brown.

Mata'utia has played more games for Newcastle (124) than any current player, and if he was to move on it would represent the end of a unique chapter in the club's history, given that his three older brothers - Peter, Chanel and Pat - also represented their home town in the NRL.

From his formative years, Sione was regarded by astute judges as the most promising of the four siblings.

After captaining Australian Schoolboys, he was asked by then coach Wayne Bennett to train with Newcastle's full-time NRL squad.

Bennett had to wait until Mata'utia turned 18 for him to be eligible for NRL selection, and he duly debuted as fullback in a win against defending premiers Sydney Roosters in July, 2014.

In the lead-up to Mata'utia's first game, Bennett made a confident prediction: "He's got a long career here, and he'll be one of the club's great players - one of this club's, and the game's."

Three weeks later, when the rookie scored a hat-trick against the Warriors, Bennett declared: "He has wonderful attributes and the great thing about him is I imagine, one day, he'll captain the Knights and be a great player here for them for all his career."

At the end of that debut season, in which Mata'utia played seven games and scored seven tries, he was a shock selection by coach Tim Sheens in Australia's Four Nations squad.

He proceeded to play three Tests on the wing in that series, becoming the youngest debutant to wear the green and gold at at 18 years, 129 days, breaking the record formerly held by Isarael Folau.

If the first few months of Mata'utia's career were a dream come true, reality soon struck.

Newcastle finished as wooden spooners for the next three seasons, and in the process Mata'utia suffered a series of worrying head knocks that ruled him out of representing Samoa at the 2017 World Cup.

But as Bennett predicted, Mata'utia captained the Knights, at 21, and he has been a fixture in the squad for seven seasons, often switching between centre and back row.

Sione's eldest brother, Peter, has been based in England for the past three years, playing for Leigh and Castleford.

The arrival of Test star Tyson Frizell from St George Illawarra will ensure fierce competition for selection in Newcastle's back row next season.