Ederson suffered the injury in a 3-2 league win away to Udinese on Sunday and tests confirmed the full extent of the damage.
"He will require surgery and will be operated on by the same specialist who tended to him in Lyon. We've agreed to have the surgery there.
"He will be out for a long time, about five or six months. It is major surgery."
Ederson suffered the injury while swiping at the ball in mid-air, but missed. He immediately crumbled to the ground writhing in pain.
Bianchini added: "The way it happened and the pain he felt, we knew immediately something was seriously wrong."