New Zealand Warriors coach Andrew Webster has confirmed star halfback Shaun Johnson has suffered a pectoral injury, with scans to determine exactly how long he will be missing for.

Speaking after another heavy loss to the Sydney Roosters on Sunday afternoon in Round 10, the Warriors' boss also confirmed Roger Tuivasa-Sheck will be out for anywhere between two and six weeks after being forced to withdraw late from the game.

Johnson played through the pain barrier in the contest, and while he avoided a ruptured pectoral muscle injury, Webster confirmed he is unsure at this stage on when the halfback will return.

"Yeah, it's a pec," Webster said during his post-game press conference.

"I Don't know if he is good for next week. He battled on at halftime. It was a tough conversation but he wanted to go on. He wanted to and fight, and I'm really proud of him for the way he wanted to go and do that.

"But as a result of where he is at for next week, or for how long, if he is out at all, I don't know."

Webster confirmed the medical advice from team support staff was that Johnson could not make the injury worse by playing on after halftime, although eventually the pain became too much for him to stay on the park.

"If there was going to be an issue there [making the injury worse] I wouldn't want him out there. If it was going to end up a ruptured pec or something like that, I wouldn't have him on the field," Webster confirmed.

"He is very sore at the moment, but it's not ruptured."

With Luke Metcalf also out of action for the time being, leaving both of the Warriors' first-choice halves out. Chanel Harris-Tavita, who would be the likely replacement for Johnson, has also been sidelined, and Webster said there was a chance he would be able to return.

"Chanel is maybe next week, definitely the week after and then we have a bye. Hopefully he is back soon but he might not be," Webster said.

If Harris-Tavita doesn't return, it's unclear who will play at halfback next weekend, with the Warriors set for a tough Magic Round tustle against the Penrith Panthers.