Injuries are never nice. I have dealt with them myself. Ask any professional or amateur, they will all tell you the same thing: being injured is the worst feeling in the world.
This is especially true for those who are just working into the peak of their careers. Extended absences can be far more damaging than just the missed development and sharpness that comes a result of them. It can lead to you losing your place in the team, it can lead to stagnation of individual progress, in some instances, it can lead to being forgotten.
That is the extreme end of the problems, of course, but every manager, international and domestic, must deal with the inevitability that some of his players will suffer injuries at times and miss significant portions of the year.