The Daily Telegraph reported on Friday that Barnett, who is contracted to Newcastle until the end of next season, had attracted a three-year offer from New Zealand's NRL franchise, who are coached by former Knights mentor Nathan Brown.

Under the NRL's free-agency rules, clubs are not supposed to approach Barnett until November 1 this year, unless the Knights have granted permission.

"I've given nobody permission to negotiate with Barney," Gardner told the Newcastle Herald.

"But the reality is agents are always out there looking around, talking to other clubs.

"We are certainly keen to extend his deal and are already looking at what we can do to keep him here beyond 2023.

"Nothing is iron-clad, but that is our intention."

Gardner said the Knights were considering a "package" that would keep Barnett in Newcastle for at least 2024 and possibly 2025.

"He's won the Danny Buderus Medal twice, which is more than anyone in my time with the club, and he's a very valued player," Gardner said. "Hopefully we can get him to re-sign before he becomes a free agent.'

The 27-year-old has played 115 NRL games for Newcastle since arriving mid-season from Canberra in 2016.

That tally would have been higher if not for a judiciary record that has cost him 12 games through suspension.

His latest indiscretion, an elbow to the jaw of Penrith back-rower Chris Smith last weekend, resulted in him being sent off and subsequently banned for six games.

Gardner said the club took into account issues like disciplinary records and injuries when entering negotiations with any player.