There are two main factors why running on a treadmill can lead to injuries.
1. The first is that the repetition factor on a treadmill is a lot higher than on the road. There are no cambers, downhills or pavements to hop on and off, so the same muscles run in exactly the same range for the entire session, which could result in injury. If your muscle length and strength were balanced, this would be no problem, but if there is unilateral tightness of fascia, it will soon show up as pain on the treadmill.
2. The second is that the surface of a cheaper or badly maintained treadmill could be quite hard, causing impact injuries such as shin splints and stress factors.
The positive side of running on the treadmill is that you can get off if you experience pain (no walking back home as with running on the road). The
treadmill teaches you to pace yourself properly and training can be well regulated, especially when coming back from injury.
Nevertheless, I find that athletes who run on uneven surfaces as in trail running are, in general, much stronger since the muscles are conditioned to work in
So yes, see that your body is properly balanced to handle the repetition on the treadmill, and then make sure you hit the off-road over weekends to strengthen and condition your muscles.