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 Saturday night’s win over South Sydney.

Cronk went for scans immediately after the game and the Roosters announced on Sunday morning they showed a severe left rotator cuff injury.

Rehabilitation has already begun on the injury and the club said in a statement that the superstar halfback would be given until kickoff next Sunday to prove his fitness.