As I always say and as I did when I trained Rozomashvili to the 9*, when one wanna train a specific pplayer, have to select other players of the reserve + subs' to train. Then if a injury have to appear the game select between all the players that we selected.
I wasted +300 greens with Rozomashvili, till he obtained the 9*, and during the training, all the substitutes + reserves, had an injury, and Rozomashvili only had 2 injuries. I posted a pic of that, so is a good strategy train players that doesnt matter if injury.