Johnson suffered the initial tear of his anterior cruciate ligament during the round three NAB Cup match against the Gold Coast Suns in March.
Sydney Swans coach John Longmire said it was an incredibly disappointing setback for Johnson.
“Alex had experienced some swelling in his knee and a subsequent arthroscope showed the graft of the reconstructed ACL was significantly damaged," he said.
“It is an extremely rare occurrence that the graft would fail in the way it has and Alex is understandably disappointed, but to his credit he is maintaining a very positive outlook.
“The Club along with Alex will now consider the best way to move forward.
“Alex is a very important player in our defence and has his best football ahead of him.”
The Club and Johnson will consult with surgeons over the next few weeks to determine the most appropriate way to proceed.
Johnson said he was disappointed by the latest news, but was looking forward to moving on with his recovery.
“It’s obviously been a pretty hard time being in rehab, and having setbacks is one thing, but to have to completely re-start again was really shattering,” he said.
“I’ve had a bit of time to get used to it and I’m just looking forward to getting to the next phase and hopefully I’ll have my surgery and then I’ll be back on the road again.”
