Yes, you can train your players daily and most of the time without injuries if you stay above 80%. At least this is what I have experienced and I have several accounts now.
Train your players to 79% or 84% or 89%, just make sure that it is 1% under what you will recover through resting - the free 5% you get back every 3 hours.
ex. I have a game at 21:13 and it is 8:22 am. My next rest is in 2hr:07min. That means that I have 4 rests or 20% recovery before the game. so I can train my players down to 79% and they will be ~99% just before the game.
I find that once they go below 80% and out of the green, they are more susceptible to injury. Others may be able to prove this or disprove it but that is how it affects me in my experience.
Ask the power trainers. They should know at what % they start to hit more injuries. But unless you power train, it is not in your best interest to go below 75% for the most part and still expect to not spend green packs to recover.