The Wellington Phoenix will be without their captain for the remainder of the A-League season.
Scans have confirmed Alex Rufer ruptured the anterior cruciate ligament in his left knee. He will have surgery in four to six weeks and faces up to 12 months of rehabilitation.
Rufer suffered the injury in the first half of Saturday's loss against Brisbane Roar when he attempted to make a tackle on Roar midfielder Rahmat Akbari.
It is a bitter blow for the 25-year-old, who has been in good form at the heart of the Phoenix midfield.
Rufer has started all 14 of Wellington's A-League matches this season, playing 90 minutes in all but one of their games during their recent seven-match unbeaten run.