The mechanics of contract discussions and injuries have always been too rudimentary for me.

I wished:
Contract discussions
Players who you “insult” too often with contract offers that are too low will eventually no longer want to talk to you at all.

Injuries
The injured player should perform worse.
If an already injured player gets injured again in a game, there should be a chance that the injury will worsen and the player will be out for an even longer period.
The risk of the player sustaining another injury more quickly should also increase.