You will want to read this thread:
Players have to actually be on the MLB 60IL in order to free a roster spot. You do not manage the IL in Ottoneu, real life teams do. There are a lot of reasons teams do not put players on the 60IL right away, even if they are hurt and have a long recovery ahead of them - mostly that they then need to make a corresponding move to fill their 40-man roster. If a team does not have anyone they want to add to the 40-man (with all that entails), they will often leave an injured player off the 60IL until a time when it makes sense.