Warriors coach Andrew Webster faces an anxious wait to learn the severity of a knee injury sustained by co-captain Mitch Barnett in their36-30 NRL win over the South Sydney Rabbitohs.

The 31-year-old was in visible pain after his right knee buckled awkwardly as he attempted to tackle Rabbitohs halfback Jayden Sullivan midway through the first half.

Barnett could be heard yelling an expletive as he managed to walk off the field, but was later seen on crutches in the dressing rooms.

Webster confirmed post-match that Barnett had sustained a knee injury but said they would need to wait on scan results to determine the severity.

“He’s definitely done a knee injury of some description,” Webster said.

“We’re waiting for scans, it’s the boring old thing - but we honestly don’t know what it is right now.

“There are different grades to each different injury and until you look under the hood, you honestly don’t know.

“He’s in good spirits, we’ll get back to New Zealand tonight and work it out tomorrow.”

A long-term injury would be a big blow for the Warriors as they continue to defy the odds this season with a 9-3 record at the midway point of the campaign, to sit third on the NRL ladder.

Barnett has developed into one of the team’s best players. Last year, he won the Simon Mannering Medal as Warriors Player of the Year, and went on to make his State of Origin debut for New South Wales and represent Australia.

Barnett also played in last week’s Origin series opener against Queensland, playing a key role in their 18-6 win in Brisbane, and the injury will cast doubt over his availability for game two in Perth on June 18.

“I don’t want to be talking like he’s not with us anymore,” said Webster.

“We lost Fish [James Fisher-Harris] for four weeks, and he’s one of the best frontrowers in the world and we know how to do next man up.

“Life goes on, but you’d rather have your best players on the field. We have the belief the next guy will do it, they don’t have to change their game, just do their job.”

Luke Metcalf scored his eighth try of the NRL season in the win over the Rabbitohs. Photo / Photosport.

The Warriors were once again made to work hard for their victory, which solidifies their spot in the top four.

Leading 14-12 at the break, they scored three tries in 15 minutes to open up an 18-point lead, before the Rabbitohs fought back to set up a frantic finish.

But the Warriors held on to claim their sixth win by a converted try or less this season.

“I’m really proud of how this group wants to work hard for each other and continue to find ways to win,” said Webster.

“That said, 18 points up, we’d certainly prefer to manage that better so there’s always room to improve.”

The Warriors are back in action on Saturday against the fifth-placed Cronulla Sharks in Sydney before their second bye of the season.

Ben Francis is an Auckland-based reporter for the New Zealand Herald who covers breaking sports news.