The latest setback on the same knee is likely to see the 28-year-old miss at least most of 2018.
"It's unbelievably sad news for Sam and his family. He has worked so hard on overcoming this injury before," Panthers supremo Phil Gould said.
"It's a huge blow for our club as well. Sam really looked like he was getting back to his best.
"As always we will ensure Sam gets the best of medical advice and care. But sometimes this game just isn't fair."
McKendry and the Panthers are seeking specialist medical advice about his best options for recovery.
The injury, while disappointing for the former Kiwi representative, could open the door for a pair of fellow Northlanders.
James Fisher-Harris and Corey Harawira-Naera, both from the Far North, may see more game time come their way.