Walker pulled up sore attempting to tackle Simi Sasagi in the in-goal 12 minutes into Sunday's game at Allianz Stadium, writhing on the ground clutching his left knee.
Three staffers attended to Walker on the field, initially calling for a stretcher.
But Walker managed to regain his footing and walk from the field with assistance, the crowd applauding as he went.
Sideline commentators reported Walker told Roosters staff he heard a popping noise on injuring his knee, usually a tell-tale sign of an anterior cruciate ligament injury.
The injury means the Roosters, set to finish in the top four, may rely on Sandon Smith to play with Luke Keary in the halves on their charge to the finals.
Jordan Rapana appears to have played his last game for Canberra. (Mark Evans/AAP PHOTOS)
Sunday's clash also appears to have been the last in the NRL for Raiders fan favourite Jordan Rapana, who suffered a fractured cheekbone attempting to tackle James Tedesco 10 minutes into the game.
Rapana appeared to wear Tedesco's elbow in his face as he tackled his rival fullback mid-air - saving a try in the process - and stemmed the bleeding from his face with a cloth as he left the field.
Given the Raiders are all but guaranteed to miss the finals, Rapana is unlikely to feature again before he moves to Super League side Hull FC from next season.
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