The 28-year-old suffered the injury to his left knee in the Knights 26-4 win over Wests Tigers on Sunday.

Initial fears of an ACL injury were ruled out during the game and while the club was hoping Fitzgibbon may only miss a few games, scans have shown the injury is a grade-three medial tear that will sideline the second-rower for an extended period.

It is yet to be determined if Fitzgibbon will require surgery to repair the injury, but either way it will be at least an eight-week recovery.

"I pretty much snapped my medial off my tibia in my leg," Fitzgibbon told Triple M radio. "It's looking like a couple of months, at least.

"It is unfortunate but there's worse things going on around me in the world. This is just another little hiccup.

"It's just the nature of the beast, rugby league."

Fitzgibbon has had a tough 18 months with injuries, reduced to only 17 games in the past two seasons.

His layoff is another injury blow for the Knights, who already have regular first-graders Jayden Brailey and Hymel Hunt sidelined for extended periods.

Starting prop David Klemmer also expects to be out for three to six weeks after undergoing minor knee surgery on Tuesday.

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