Essendon can confirm Patrick Ambrose has suffered an injury to his posterior cruciate ligament (PCL).
The defender sustained the injury during the Bombers' practice match against Melbourne on Friday.
General manager of football Dan Richardson said the club would meet with a specialist to further assess the injury.
“Scans have confirmed the views of our medical team that Paddy suffered an injury to his PCL during a marking contest in Friday’s practice match,” Richardson said.
“The Club will consult with a specialist in the coming days.”