Sydney Roosters playmaker Luke Keary left the field against the Newcastle Knights on Saturday afternoon and is feared to have a fractured jaw.

Attempting to make a tackle, the five-eighth collided with the heel of Dominic Young.

Keary was coming across in cover defence but the speed of Young was too quick, meaning when he dived he colided into the winger's boot in a freak accident.

Visibly in pain, Keary left the field immediately and was later seen in the changing room still in pain.

"Luke Keary, fears that he has fractured his jaw," Fox League sideline commentator Lara Pitt said.

“Just a horrible moment in the Roosters season,” commentator Warren Smith said on Fox League.

Drew Hutchison took over Keary's role as five-eighth after he left the field and is partnering with Sandon Smith in the halves.

It is a massive loss for the Roosters, considering halfback Sam Walker is also out with a knee injury.