Normally, this shouldn't be such a big problem. If you want your player to play the whole game, just put them in their position all the way through the depth chart. If you want to play them anything lower, however, the amount of playing time they get is based on how good your subs are compared to your starters (if they're both the same skill, the starter will get about 28 minutes. If the starter is by far better than the sub, he'll play about 42 minutes a game.)