Shaun Johnson's Warriors season is over - and the star halfback will also miss the Kiwis' World Cup campaign.

In one of the biggest blows possible for the player, his club and the code, Johnson has ruptured his anterior cruciate ligament and faces at least seven months on the sidelines.

The 26-year-old will have scans tomorrow, but the Herald on Sunday understands the club is "99 per cent certain" Johnson has torn his ACL.

After surgery, which Johnson will have in two or three weeks, there is a minimum rehabilitation period of six months, and possibly more.

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It means Johnson won't feature for the Warriors again in this campaign, and will still be on crutches during the World Cup, which starts on October 27.

It continues a luckless run for Johnson, who snapped his ankle ligaments at almost the same stage of the 2015 season.

It also continues a cursed period for members of the Warriors spine, with Thomas Leuluai (2015) and Roger Tuivasa-Sheck (2016) also suffering ACL injuries.

The injury happened midway through the second half of the Warriors' 34-22 loss to the Panthers on Friday night, and similar to the cases of Leuluai and Tuivasa-Sheck, looked fairly innocuous at the time.

Johnson was chasing an Issac Luke break when he pulled up suddenly, grimacing in pain.

Coach Stephen Kearney is braced for the worst scenario. "He'll get some scans but the early diagnosis is probably not a real good one," Kearney said.

"Potentially [it could be serious]."

It could also be a terminal blow for the Warriors' already slim finals hopes. The meek defeat at the hands of Penrith put their top eight prospects into "mission impossible" territory.

For all the criticism Johnson can attract, it's a fact that historically the Warriors simply haven't coped without him for long periods. They fell apart in late 2015, losing seven consecutive games, after he was ruled out for the season.

Kieran Foran's presence will help this time, but the former Manly and Parramatta player has been inconsistent over the past month.

Likely replacement Ata Hingano is a player of great potential but will be on a steep learning curve over the next six weeks.

Johnson's absence will also put more pressure on the Warriors' pack.

Without Johnson's long kicking game and ability to conjure breaks and tries from all areas of the field, the Warriors forwards will have to dominate to give their team any hope of success.