I am looking for an idiom for a creature/person we choose to sacrifice in a tough situation. We choose that creature/person because we have to choose one, and that creature will cause the least trouble for us (defenseless maybe). The others might cause noise, hassle, ... etc.
In an example, let us say you are an employer, you want to lay off one employee. You choose the one who will cause less disruption. What can I call that employee? Scapegoat came to my mind. But, to me, scapegoat is a person who is blamed for other's mistake. Here, I am referring to no mistakes. It is just harsh circumstances, and you decide to sacrifice that person. I can only relate to evolution theory when a mother kills the weakest baby to survive a harsh winter, knowing the food will be scarce.