Devastatingly for McKendry, it is the third season in a row that's been ruined by ACL injuries.

He suffered the tear while being tackled in the 42nd minute of Saturday's game at Panthers Stadium.

"It's unbelievably sad news for Sam and his family," Panthers executive general manager Phil Gould said.

"He has worked so hard on overcoming this injury before. 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."

A New Zealand international, the front-rower debuted for Penrith in 2008. McKendry has played 147 NRL games for the Panthers and eight Tests for the Kiwis.