The Knights confirmed on Thursday that Gagai was out of the 4.05pm (AEDT) match at Go Media Stadium in Auckland.

Football director Peter Parr told the Newcastle Herald Gagai was dealing with a medical condition but did not expand on the issue.

"He is out and we will finalise the team once in New Zealand," Parr said.

"We're not sure yet what we'll do with the team, there's a few options there.

"He has a medical condition, and that's of a personal nature. He'll play against the Dragons [next week]."

Gagai has played every minute of Newcastle's three games this year, and also played in the NRL All Stars fixture in February.

He scored a try in Newcastle's 14-12 win over Melbourne last round.

The Knights fly to New Zealand on Friday.

Dylan Lucas, who was named 18^th man this week, appears most likely to take Gagai's spot.

The only other outside-back in the extended match squad is Will Pryce.

The Englishman is yet to make his NRL debut but has been impressive in NSW Cup in the opening rounds.

Pryce has limited experience at centre in the Super League, while Lucas previously played there before transitioning to the back row last year.

Lucas was forced to shift to right centre and Gagai to the wing in round one after winger Enari Tuala suffered an injury.

Tuala returned last week, but the Knights remain without winger Greg Marzhew (wrist) and centre Krystian Mapapalangi (shoulder).

They also lost prop Leo Thompson this week after he accepted a one-match suspension for a dangerous contact charge.