I don't know about Fred under ETH's rule. Fred is not the kind of player to come off the bench and be a game-changer. His contributions are usually not that clear cut (goals, assists). He doesn't look after the ball well, or at least not as well as players like Matic and Pogba do, where they can receive it under pressure and not cough it up due to poor control. Fred can be pretty wild with his first touch, control, and passing, offers little goal threat. So if he's not looked at as a starter, he should be off. Yes, he's a trier, yes, he doesn't shirk his responsibilities, but he's not good enough for a starting XI that is competing for anything, and as a sub, he's too erratic to come on and either see out the game or help get the winner.
I say move him on.