If the manager really did try to correlate the squad size to the number of injuries he'd notice the last time we were relatively injury free was when we had a tiny squad. So hopefully he doesn't actually do that. We also rotated our squad, a lot. The second string were not particularly good, but the were used.
Can't comment on training but I think a lot of our problems comes from rushing players back and putting them right into the thick of things. Maybe I'm remembering incorrectly but didn't we used to ease players back in with reserve games or subsitute appearances back in the day? How often do we get these 'set backs'? Seems to happen a lot.