I'm far from an expert, but I've asked some questions about playing with no draft before...
In
this thread Questdog told me that when you play with no draft, new players are created on the first day of the offseason. I haven't experimented enough to know whether the game only creates players if you "need" them, but if you know when they are coming in, you could take measures to control their introduction by deleting those that you don't want.