Queensland halfback Johnathan Thurston is relieved to avoid surgery but will miss up to six weeks of NRL action after scans revealed medial ligament damager suffered in Wednesday night's State of Origin decider.

Thurston admitted he anticipated the worst case scenario of a season-ending injury when he was felled in a sickening collision with Maroons team-mate Ashley Harrison in the second half at Suncorp Stadium.

"I was in a fair bit of pain ... I thought it might have been my ACL (anterior cruciate ligament)," Thurston said on Thursday.

"It looked a lot worse than it is."

Thurston met with orthopaedic surgeon Peter Myers who delivered the good news that it was a grade two medial ligament tear and bone bruising which would put him out for just six weeks.

But the North Queensland co-captain instantly set himself a challenge of returning in four.

"I wasn't really contemplating anything until I had seen Pete Myers and he assessed the knee and had a look at the scans," Thurston added.

"He reckons I'll be back out on the field in six weeks, I'm pretty relieved and I had a big smile on my face.

"I've just got to get into rehab and get back in four (weeks)."

While he doesn't need surgery, Thurston will wear a brace and will be out of NRL action for North Queensland until at least their clash with Brisbane on August 12.

And despite the setback, Thurston backed his team-mates to continue the Cowboys strong form in his absence and said he would be back in time for the finals.

"Sitting on the sidelines is the hardest thing to do," he said.

"I've been in this situation before and I know what to expect and I know how hard I need to work to get the knee right and be back in the amount of time I want to be back."

Thurston's Cowboys co-captain Matt Scott said the whole squad had a responsibility to step up while their inspirational captain was sidelined.

"It's a lot tougher," he said.

"Any side's main ballplayer, main halfback is going to be a massive loss but we're in a pretty good position at the moment sitting fourth on the ladder.

"We've just got to keep playing good footy without him and hopefully we get him back in six weeks leading into some finals footy."

No decisions have been made on a replacement halfback for the Cowboys-Newcastle game on Monday night.

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