Halfback Nathan Cleary has been ruled out of the Pacific Championships Test series with a knee injury he picked up during his heroic NRL grand final performance.

Cleary allowed centre Stephen Crichton to convert the first try in the 17th minute of the grand final against Brisbane as the trainer looked at his left knee.

The 25-year-old could be seen limping during the first half, but recovered to kick four more goals and play a pivotal role in the Panthers' sensational comeback win against the Broncos on Sunday.

But Cleary, who usurped Queensland captain Daly Cherry-Evans in the starting side during last year's Rugby League World Cup, will miss the Kangaroos' inaugural Pacific Championships campaign after succumbing to the injury.

Sharks half and 2022 Dally M Medal winner Nicho Hynes will replace him in the squad for the four-week tournament, with Australia playing Samoa on October 14 and New Zealand on October 28, before a potential final appearance the following weekend.

Also appearing in the tournament are Cook Islands, Fiji and Papua New Guinea, with games in Townsville, Melbourne, Port Moresby, Auckland and Hamilton.

Cleary's withdrawal leaves premiers Penrith with just two players, Liam Martin and Isaah Yeo, in the Kangaroos' 21-man squad.

Cherry-Evans and Cameron Munster will likely be the first-choice starting halves, with Hynes and Ben Hunt also able to play in the six and seven.