Johnson, who was a key player in the Swans' 2012 premiership, suffered the injury during the round three NAB Cup match against Gold Coast nine days ago.
The 21-year-old returned home to Melbourne to contemplate his treatment with family and friends and opted for a traditional reconstruction instead of LARS reconstruction surgery.
Johnson played all 25 games last season and conceded more than two goals on only two occasions.
A brilliant reader of the play and strong tackler, he will sorely missed in a Swans backline that ranked No.1 last season for points conceded.
