Milera sustained the injury when he landed awkwardly from a marking contest during Friday night's loss to Fremantle at Optus Stadium.
It is the same as the injury Milera previously sustained in his left knee, which ruined his 2021 season.
The 26-year-old, who has played 99 AFL games, will undergo surgery to repair the damage in the coming days.
"It's obviously devastating for Wayne, who has dealt with his fair share of unfortunate injuries in his career so far," Crows high-performance boss Darren Burgess said.
"The surgery will mean he will miss the rest of the season while focusing on his rehabilitation.
"Unfortunately, he has been through this before, so he knows the road ahead.
"But as we know with Wayne he is a very strong, positive person who will do everything to ensure he returns bigger and better next year."
Adelaide were already without Nick Murray (8-10 weeks) and Riley Thilthorpe (10-12 weeks) because of long-term knee injuries.
There is no time-frame yet on Rory Sloane's recovery from an eye injury, while Harry Schoenberg (achilles) is out for at least another month.
Milera's latest setback comes during a tough run for the Crows, who have opened the season with three straight losses.
They face a huge challenge against Melbourne at Adelaide Oval on Thursday night in the opening match of Gather Round.
8°C