Penrith and New South Wales' star Jarome Luai is in doubt for State of Origin Game 3 after scans on his knee returned.

Luai played out Penrith's Round 16 game against the Panthers, but had a noticeable limp after suffering a knee injury in a tackle during the second half from Tom Opacic.

The number seven said post-game that he expected it to only be a cork, but scans returned on Saturday evening showed an MCL injury.

It's understood Luai will wear a brace for the next week, and is now in extreme doubt for Origin 3. The Panthers are reported to have informed the New South Wales Blues' hierarchy of the news late on Saturday.

The news is about as bad as it possibly gets for New South Wales, with Brad Fittler's side already missing Nathan Cleary for the dead rubber, who will miss six weeks with a shoulder injury during Game 2 of the series.

The club combination of Cleary and Luai has been superb in guiding the New South Wales outfit to a combined 76 points to 6 scoreline against the Queensland Maroons across the first 160 minutes of the series.

Speaking on Fox Sports' coverage of the Raiders and Titans, Greg Alexander said Jarome Luai has suffered a Grade 2 medial ligament injury and would miss the game.

With Luai now in doubt, Brad Fittler will need to find two cover options. Adam Reynolds and Moses Mbye were thought to be the front-runners to replace Cleary, and while it could be tempting to play both of them, Canberra Raiders' ball-runner Jack Wighton has played the opening two games from the pine and could come into the starting side now alongside one of the favourites.

The New South Wales side is expected to be named on Sunday evening, although with injury news and camp not commencing until Tuesday, there is a chance Fittler and his staff may hold off until Monday morning, as Queensland have done for the first two games.