The primary factors to consider are the severity of an injury and the composition of your bench. The schedule for fantasy football is brief compared to other sports, so an injury with a lengthy recovery (i.e. torn ACL or ruptured Achilles) requires an owner to swap the affected player for a healthy one immediately. In some cases, it's prudent to look at the teammate who replaces him, but typically the best player available at his position in the free-agent pool is the first one to attempt to pick up. For a lesser injury - one with a recovery expected to be weeks instead of months - an owner usually can get by with stashing a top-level player, unless bench spots are at a premium. If your league offers an injured reserve (IR) spot then you can move an injured player to that spot until he returns, opening up a roster spot to add a free agent.