The Sydney Roosters have broken their preliminary final hoodoo and are on their way to next Sunday's grand final against Melbourne at ANZ Stadium, but they may be without chief playmaker and former Storm halfback Cooper Cronk.

The three tries to none 12-4 win over arch rivals South Sydney had all the drama befitting the final game to be played at Allianz Stadium before the bulldozers move in. It was witnessed by the venue's largest crowd for a sporting event in 30 years – 44,380.

But while the Roosters had lost three preliminary finals since their 2013 premiership, the real story of their courageous win on Saturday night was Cronk.

The former Test halfback played the entire second half with one arm after he hurt his left shoulder in a missed field goal attempt in the shadow of the half-time siren. The tackle by his opposite No.7 Adam Reynolds was completely legal but Cronk hit the ground hard.

He left the field with his left arm dangling by his side. Internal cameras had vision of Cronk lying on a massage table in the Roosters sheds at the break with physios treating the joint and strapping it.

His match-up against the club he won two premierships with (2012, 2017) is highly anticipated. But the severity of Cronk's injury is the big question.

Cronk injured

Roosters coach Trent Robinson said Cronk would have scans as soon as possible but he expected him to play next Sunday after intensive treatment and quality rest.

"Obviuosly ice, and he'll go and get scans," Robinson said. "I know you want information straight away and after the scans we'll know more.

"I'd say he'd be right to play next week though."

Robinson said there was no thought at half-time to rest Cronk for the remaining 40 minutes of the match.

"No, definitely not," he said. "It wasn't even discussed. To be honest, I didn't even ask how he was.

"Cooper knows how he is and he needed to get work done [on his shoulder] at half-time. He was always going to go back out there but it looked pretty sore."

Captain Boyd Cordner said his teammates noticed how bad Cronk's injury had become late in the game.

"You probably wouldn't expect anything less from Cooper... anyone who's ever played with him knows he's one tough guy who'd do anything for his teammates and anything to try and get the win."

Rabbitohs coach Anthony Seibold was asked why his South Sydney forwards didn't target an obviously hampered Cronk more often.

"What, spend your life targeting Cooper? I don't understand. He was still making his tackles," Seibold said.

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"Where we needed to be better was execution in attack. We didn't get to the right areas of the field we wanted to run our shapes from.

"We didn't necessarily look to chase him. We wanted to put him under pressure when he kicked the footy. That [Cronk injury] didn't have any impact on the game.

"Probably we weren't the best version of ourselves tonight either so that's also what makes it disappointing."

Maybe they won't need him as his halves partner Luke Keary stepped up and took over the majority of field position and attacking kicks.

It was a Keary corner kick that brought stand-in centre Paul Momirovski the Roosters' third try of the game, which ended up being the match-winner.

All eyes and ears will now be on the medical reports for Cronk.

Robinson confident Cronk will play Grand Final

He returned to the field in the second half but his left arm was still limp. He made a few tackles but couldn't kick the ball.

Jake Friend kicked for touch on the fifth tackle – but it sailed out on the full – in the 42nd minute while Luke Keary kicked for the line in a penalty two minutes later, and took over end-of-set kicks.

Passing to his left also had its difficulties with Cronk not able to get much distance. But he did figure in Blake Ferguson's 48th minute try, although it was the Roosters right-side winger that did the most work.

He took an off-load from his centre Joseph Manu and then side-stepped two cover defenders to grab his side the lead 8-4.

A late tackle by Junior Tatola brought Cronk to his knees and a penalty the Roosters way. But he soldiered on to complete the 80 minutes.

Scores were locked at 4-4 at the break.

Cronk tried to break the deadlock with that field goal attempt 20 seconds from the halftime siren, but it drifted slightly left.

The Roosters scored the only try in the first half (15th minute) and it was a beauty. From crisp passing by halves Cronk and Keary, fullback James Tedesco then added his own exclamation mark with a sublime cut-out pass for winger Daniel Tupou.

All Souths points were by No.7 Adam Reynolds with two penalties.

Ball control and big hits was the order of the day early.

Various combinations of the Burgess brothers forced the ball from Jared Waerea-Hargreaves and Paul Momirovski's grasps in a bruising opening 10 minutes. Waerea-Hargreaves got one back when he forced George Burgess to knock-on from the re-start to a Reynolds penalty.