If it dislocates. I agree with the above. In certain cases where there is more trauma and a dislocation occurs both ligaments can be torn at the same time. Fortunately this is uncommon, but there are some serious potential neurovascular side effects with the type of injury.
Yes. It's not uncommon for an athlete to have a knee injury involving multiple ligaments and/or menisci, possibly partial or complete tears. Pcl is considered the strongest ligament in the knee, and it's the least frequently injured ligament. Isolated PCL tears occur less frequently than combined ligament tears such as tearing of the acl and PCL at the same time.