Bills Post Game Massacre. U like thats and dislikes

[SolidSnake84]

Here is a question that i don't really have an answer for:

Seeing all of the guys who are "day to day" on injury report, WHO actually makes the decision on if a player plays or not? Is it the team doctor? or the player?

Say for example someone like Alfred Morris has some kind of injury, let's just say it is his knee. Medical logic says he should set, but what if Morris was just 100% dead set on playing and helping the team? Could he make the decision to play on a bad knee / play injured, etc? Or does a higher power so to speak rule him out???