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For a fourth time Knights coach Adam O'Brien has to reassemble his spine due to the likelihood of a season-ending ACL injury to five-eighth Blake Green.

The mid-season recruit limped from McDonald Jones Stadium in the 18th minute of the 12-0 win over the Cowboys in just his third game with the Knights after leaving the Warriors and the prognosis doesn't look good.

But following an ACL to first-choice hooker Jayden Brailey, and then a serious hamstring tear to replacement rake Andrew McCullough on top of a torn Achilles tendon to utility Connor Watson, O'Brien is again pondering who will fill the No.6 and No.9 jerseys.

Kurt Mann has been doing cameos in and out of those positions, with Phoenix Crossland coming off the bench to play 63 minutes at hooker in Sunday's win over the Cowboys.

"He did a really good job in that No.9 position for the amount of minutes he had to play. He's never had to do that before," O'Brien said.

Green leaves field with knee injury

"Just looking at him in the sheds he's battered and bruised. He's a young man and we expect him to hold his gloves up again next week for us."

Crossland is unlikely to be given the 80-minute assignment in the hooking role so O'Brien will have to work out a plan to use Mann to share the dummy-half duties or bring utility options Mason Lino or Tex Hoy into the squad.

"I'm not too sure [about spine]. I'm going to have a meeting with the coaches after this and see what we can do there," O'Brien said.

"We've got some options with young Mason [Lino] and Tex [Hoy]. We'll see what we come up with."

Knights: Round 15

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Asked if Kalyn Ponga was a chance to slip back into five-eighth, where former coach Nathan Brown briefly played him last year with limited success, O'Brien batted that idea down quickly.

"I think this late in the season that's too many changes. He's doing a really good job for us at fullback," O'Brien said.

Another injury concern is NSW Origin prop Daniel Saifiti (left knee) who missed the Cowboys game and appears unlikely to be back to face the Warriors in Tamowrth next weekend.

"He will be very close but close won't good enough. He needs to be 120% or I won't play him," O"Brien said.

"The guys in the forward pack did a really good job tonight."

Get Caught Up: Round 15

It was just two tries – both off final passes from Kalyn Ponga – so the attack wasn't up to usual Knights standards.

But with three key positional changes O'Brien was more than happy about how his men coped.

"We need to get better in some areas obviously but I'll take the toughness and grit. That's what we wanted at the start of the year."