Cody Walker has been taken from the field in agony by the trainer in the first half of the Rabbitohs and Knights clash, with a suspected calf injury.
Just 10 minutes before half-time, he was aiming for a tackle and fell to the ground in a non-contact situation, remaining down after the Knights continued to break through the line.
Walker immediately signalled to the trainer that he was gone for the game.
Immediate fears for an achilles injury were proven likely incorrect, with South Sydney fearing a calf problem.
"From what I can understand from the Rabbitohs bench initially, they are thinking it's a calf for Cody Walker that will rule him out for the rest of the game," Eloise Sohier said on the sideline for Fox Sports.
"He walked straight past me and just couldn't control his emotions, in tears."
It is a devastating blow for the Rabbitohs, who are heading into halftime 10-6 down.
Walker's injury is all the more emotional as his playing future at South Sydney is uncertain, off contract at the end of this year.
The early departure could signal the end of his Rabbitohs and NRL career with retirement an option.
Jamie Humphreys will replace Walker at five-eighth for the remainder of the match, not only fighting for a win but a contract extension at the Rabbitohs, as he is off contract at the end of this season.
The Rabbitohs, who endured a start on the back foot, scored through Campbell Graham not long after Walker's injury to go into halftime behind 10 points to 6 against the Knights.
