Former Kiwi prop Sam McKendry has had a third straight NRL season at Penrith ruined by a knee injury, after scans revealed a torn anterior cruciate ligament.

McKendry injured right knee in the Panthers' 18-14 win over South Sydney on Saturday, and while he played on for 12 minutes after he went down, scans have since revealed a tear.

It comes after he missed the second half of the 2016 season after he tore his right ACL for the first time, before re-injuring the same knee at the start of last year and sitting out the whole of 2017.

The latest setback on the same knee is likely to see 28-year-old miss at least the most part 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.