I cant remember if this is already a thing. But if not, having player get seasonal fatigue that not only relates to injuries but also performance.
If a QB throws x amount passes every game they start to fatigue from game to game. Or a RB has x amount of carries every game, they start to slow down and become more injury prone as the season goes on unless they get a breather in the number of carries. Maybe a combo of their speed, accel and strength would factor into it.
It would have to be taylored by position to mimick RL somehow. Maybe it's already being done or maybe it's not possible to code. But I think it would add another layer to how a GM game plans. Especially early in the season.