Sydney captain Callum Mills will play no further part in Sydney's qualifying final against Brisbane.
He came from the ground early and was unable to weightbear on his right knee as two trainers helped him off.
There are fears he may have suffered an ACL rupture but the Swans could not confirm the severity of the injury.
The incident occurred deep in the first quarter, with Mills' knee collapsing from under him as he attempted to change direction to pressure Brisbane's Will Ashcroft.
Minutes after he came he was limping around on the boundary line before promptly going down to the race.
It came after a hot start for the Swans, whose marking forwards took full toll on a shaky Brisbane defence.
More to come
