Injuries are unfortunately very common in top eleven and can occur in large frequencies in real life as well, You only have to look at Arsenal's recent injury list over a number of seasons to see how often they occur, Also if your a lower level manager on top eleven injuries are very common, simply because the clubs don't have good facilities and also the players qualities are low that they arent as efficient as higher rated players at avoiding injuries, but at least on top eleven you do have the power to heal injuries instantly like they didnt happen with medic packs but if you don't have many medic packs then you need to use them wisely.