I'm quite certain he starts opening day. Very slim chance Hoke doesn't let a senior RB, who was a starter as a junior before injury, be the starter on opening day. Maybe if there were other factors like off-field behavior or injury, but Fitz will start without question if he is healthy and he has shown good behavior. Green could start at some point in the season, but opening day is for Fitz, I don't care how good the freshman is. That is why Hoke is loved by his players, he respects who they are and what they have done for the team throughout their career.
I know freshman will start, but not over seniors who were starters as juniors.