NSW assistant coach Trent Barrett says Glenn Stewart will be given as long as possible to prove his fitness for the State of Origin decider in Brisbane.

Stewart was carried from the field just before halftime against Melbourne on Monday after injuring the medial ligament in his left knee in Manly’s 26-22 loss at Brookvale Oval.

The initial prognosis is that the back-rower will be out of action for up to three weeks, which would rule him out of the July 4 clash at Suncorp Stadium.

However, Barrett said Stewart’s influential display in the Blues’ win in Sydney last week make him a key part of Ricky Stuart’s plans and he would not be ruled out immediately.

“It didn’t look very good but fingers crossed he’ll be okay but if not we’ve got a bit of depth in that area,” Barrett said.

“We’ll be okay but he’d be a huge loss. He’s a very important part of our side.”

Melbourne’s Ryan Hoffman and St George Illawarra’s Beau Scott would be candidates to replace Stewart, as is his Manly teammate Tony Williams who is recovering from a back injury.

But Barrett said Stuart wouldn’t consider any other player until the full extent of Stewart’s injury is known.

“Ryan’s there and there’s also Beau Scott who has been there and done a terrific job for us before and T-Rex may be fit,” Barrett said.

“We’ve got some options but we won’t go down that path until we know 100 per cent what’s doing with Glenn.

“We’ll be guided by Glenn. He’ll know if he’s going to be okay or not.”

Barrett also said seeing skipper Paul Gallen and Anthony Watmough get through last week’s game without any training would stand Stewart in good stead for selection.

“Because he’s an experienced player, we would certainly give him up until the day before the game to play,” he said.

“We’re lucky he is experienced and he’d know how to handle himself mentally for the week.

NSW back-rower Luke Lewis said the loss of Stewart would be a massive loss to the side.

“Hopefully the scans come back and show it’s not too bad,” he said

“We’ve got a great bunch of blokes and everyone gets on well and it wouldn’t be the same without him.”

“I’m sure everyone in the squad has their fingers crossed that he’ll be there.”