Percival was injured in Thursday night’s loss to Salford. Saints coach Keiron Cunningham confirmed that Percival will be out for some time.
“Percy is not good. You won’t see Percy for a couple of months,” he told Love Rugby League.
“He’s worse than what he was last year when he did it. It’s not good for Percy.
“It’s unfortunate for because he was going good, he was training hard and now we’re back to square one and we have to start again.
“He’s ruptured his medial ligament. He’s going to be a while.”
The fullback has been out since June after snapping his Achilles tendon.
“He’s going really good, he’s going really really good,” Cunningham enthused.
“He’s a matter of weeks off now. If you would have asked me that a couple of weeks ago, Shannon was in a pretty bad spot.
“He’s actually made great strides in the last month. I’m pleased for him. He’s worked really hard and deserves to get back.”