Newcastle's 22-14 win secured a grand final place, but hooker Phoenix Crossland was sent off for a hip-drop tackle on Nathan Cleary.
Cleary suffered a compound fracture and dislocated ankle, requiring emergency surgery.
On Monday, Cleary confirmed Crossland had apologised, then urged people on Instagram to stop abusing him ahead of his judiciary hearing.
The online attacks included claims the tackle was deliberate and threats against Crossland, the Knights' dummy-half.
"It was a complete accident and he doesn't deserve the unwarranted hate," Cleary wrote.
"He reached out to apologise and I have nothing but respect for him."
Crossland was referred directly to the judiciary, which can consider Cleary's injury.
He is likely to miss Sunday's grand final against the Sydney Roosters, and the suspension could affect his World Cup campaign with New Zealand.
The longest ban for a hip-drop tackle is five weeks, which would keep Crossland out until the World Cup final if New Zealand qualify.
Knights coach Justin Holbrook said Crossland was disappointed and added, "He's been so great for us every week this year."