Doctors make a huge difference. Never have a doctor lower than 4.
Apart from that, injuries really suck and do not contribute for manager's motivations. I agree this is supposed to be a simulator and injuries happen in real life but this is not real life, this is something you do for pleasure while doing all the other stuff also called as "getting a life". Injuries don't add anything positive, they just bring negativity and frustration. It's not like training, which can be painfully slow but also can be extremely rewarding. Injuries just purely suck. They only don't suck when they happen to a rival, but that is the kind of thing that also suck. So I think injuries should just be abolished from this game, or reduced to 4 matches maximum, instead of 4 weeks maximum.