The full extent of Cooper Cronk's shoulder injury revealed

Scott Bailey and Steve Zemek
The full extent of Cooper Cronk's shoulder injury revealed

Cooper Cronk's race against the clock to be fit for the NRL grand final has begun after scans confirmed a serious left shoulder injury suffered in the Sydney Roosters' win over South Sydney.

Cronk will be given until kick-off next Sunday to prove his fitness, after it was revealed he'd suffered a "severe left rotator cuff injury" in the 12-4 preliminary final win.

Rehabilitation began almost immediately for Cronk, who spent the majority of the second half with his left arm hanging by his side.

Brought to the Tri-colours to win a premiership, the 34-year-old must now defy the odds to play in the decider against his former Melbourne teammates.

Cronk copped a shot from Sam Burgess during the first-half before being ironed out by opposite No.7 Adam Reynolds as he took attempted a field goal on the half-time siren.

Cronk looked like a sitting duck in defence as he struggled to raise his arms to tackle.

Scans have revealed Cooper Cronk has a "severe" shoulder injury.

At one point he was thrown the ball to take a kick for touch and could be seen telling his teammates: "I can't".

However, Roosters coach Trent Robinson insisted Cronk would be available to play in his third consecutive grand final, chasing back-to-back titles.

"I'd say he'd be right to play next week though," Robinson said on Saturday night before seeing the scans.

"It wasn't even discussed (taking him from the field). To be honest I didn't even ask how he was.

"Cooper knows how he is. He needed to get work done (from the medical staff) there at halftime and he was always going to go back out there.

"But it looked pretty sore."

If Cronk is ruled out, it's likely Ryan Matterson would slot into the halves as he did during five-eighth Luke Keary's knee injury last month.

Back-up half Sean O'Sullivan would then be a likely option on the bench.

Cronk was at least protected by his defenders around him in Saturday night's win, forced to make just 11 tackles by the Rabbitohs - with only five of those in the second half.

Burgess ran at Cronk on a couple of occasions while Junior Tatola whacked him with a late shot, for which the Rabbitohs were penalised.

Robinson praised Cronk's teammates for getting around him and acting as his bodyguards.

"You saw (Mitchell) Aubusson and the work that he did really tirelessly in and around Cooper," Robinson said.

"And also Joey Manu, he made some big efforts in and around Cooper.

"They're a pretty tight bunch and you could see their work ethic."