To be honest, I'm not interested in doing that to confirm they are in the game and have people say "see they're there"; the aim was to see if they could be triggered by normal/approximately normal gameplay and I am satisfied that they cannot be.
The batsmen gets a very small fatigue penalty for being hit, so my guess is if you max out their fatigue a hit injures them. There didn't seem to be a multiplier effect whereby hitting them several times in short time increases the fatigue penalty, and the fatigue from the hit dissipates quickly. In practical terms you're probably talking circa 100 consecutive hits to max out the bar...
So as said above, in respect of normal gameplay then in practical terms injuries don't exist; remember that batting (even running) doesn't take much out of the batsman and he gets "rested" at intervals so again normal batting won't fatigue them to a state whereby one hit will injure them.
Let's be honest the game has been out a year, everyone here has hundreds and hundreds of hours of game time and nobody has reported seeing an injury; I don't think I risk contradiction when I say that playing under normal circumstances you will never see an injury.