The 20-year-old left the field in the last quarter of Fremantle’s 21-point win over the Sydney Swans at Subiaco Oval on Saturday night and did not return.
Palmer had scans of the knee taken on Sunday and when they were reviewed on Monday by Fremantle medical staff it was established that his ACL was “abnormal”.
An orthopaedic surgeon who was called in to further review the scans diagnosed a near complete tear of the ACL.
General manager of football operations Chris Bond said that Palmer would undergo surgery late this week or early next week.
It was initially thought that Palmer had avoided any major damage but the extent of the injury was unable to be determined at the time because it was not a complete tear of the ACL.
“It is very disappointing for Rhys and the club,” Bond said of the season-ending injury.
“But we are very confident that after the appropriate period of recovery and rehabilitation, Rhys will be back playing the brand of football we know he is capable of.”
Palmer was awarded the Ron Evans Medal for the NAB AFL Rising Star for his outstanding debut year in 2008.
He won with 44 votes from Hawthorn's Cyril Rioli (37) and Richmond's Trent Cotchin (21) to become the 16th winner of the award.
