Are the Spanish players on your game extremely thickle?

I am playing as the Spain national team manager. But every time I comfirm the squad I want, I always get a message later on saying one of them is injured. Most of the time I get like two or three of them injured and I have to call up a replacement. And most of the players being replaced are already replacements themselves for other injured players. Its not that much of a bad thing though. It gives me a chance to call up players who normally wouldnt get a chance to play for Spain. I have had Arteta in my last few squads. It was nice to have a chance to give him his first cap.

I am currently on my second demo save as Athletic. In both saves, Mikel San Jose was called up for Spain and both times he injured himself in training and had to be removed from the squad...

I think you mean fickle, (which means unstable + irrational), but if your question is: Do they get injured a lot? then my answer would be no more than any other nationality.