The first few levels it can be cheaper to buy than heal for sure.

Keep in mind even if it's a broken leg, 15 reds is the most it will ever require, so if it's a key player, it could be worth healing.

When you have two matches a day, only do the training to even out condition, as little as possible use the stretch if you want to lessen training injury odds a bit. Also, upgrade your turf as much as you can.