The 23-year-old Lousi, who was used off the bench in the 24-42 loss to the Titans, had scans yesterday.
We initially thought there was a possibility Sione had damaged his posterior cruciate ligament but unfortunately scans have confirmed he has ruptured his ACL, said Vodafone Warriors doctor John Mayhew.
Hell have surgery in about two weeks once the swelling has gone down.
Head coach Matthew Elliott said everyone at the club felt for Lousi.
Its devastating for him but hell have every support we can give him, he said.
Well ensure hes kept occupied throughout and have every hope well get him back on the field before the end of the season.
As well as working through the physical side of his rehab, were going to involve Sione in studies to keep him busy.
Lousi played 22 of the Vodafone Warriors 24 games last season, boosting his career tally to 31 since his debut in 2012.
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