Here's a suggestion I posted on the MZ forums...
I'm sure player contracts has already been suggested, but I'm mentioning it again, in combination with another suggestion I haven't seen posted.
What I had in mind was a more robust player AI, where players would be on contract, and it would be up to the manager to negotiate a new contract before the current one expired. Meanwhile, similar to the current system in place for trainers, the players would be free to negotiate new contracts with other clubs. The manager would have the added responsibility of having to sweeten the deal just enough to keep the player loyal to his club.
I would propose a new player attribute be added, called "Morale". This would be a reading of a player's happiness or displeasure with his current club. Certain things would affect a player's morale, e.g. how much playing time they are receiving. This could give a manager some sort of indication on how well his contract negotiations might fare. Naturally, a manager will have to work extra hard in trying to re-sign a player with very low morale. A low morale could lead to other things, such as a player letting you know he no longer wishes to play for you and wants to be put on the transfer market. As is the case with form (at least I think it is), a player's morale will also affect his other attributes, e.g. a player with high morale will try harder to make that tackle or that cross.
A third suggestion would be player loans. As an example, a club has a promising young player, but they do not have room for him on the first squad, and they do not want to sell him, knowing his potential. Instead, the club loans the player to another club who is looking to fill a void.
What do you guys think?