Not sure if this one has been brought up yet or not, but....
Every sports simulation or video game I play always has crystal clear return dates on injuries. Example: In HBD, a guy gets injured for 8 days, or 22 days, or 81 days.
I want to see injuries where the return date is to be determined by ME, the general manager. A guy sprains his wrist, he'll miss a minimum of 10 games, but after that you have the option to bring him back though he's not fully healthy or let him rest longer. Of course, if you bring him back his ratings won't be fully recovered, he risks further injury making it worse, and his recovery takes longer--maybe after 10 days of rest he'll need 15 more days to fully recover, but since he's playing instead of resting it'll take 30 more days to fully recover--but at least he's in your lineup.
Taking it a step further, some injuries that may or may not require surgery can fun. You can opt to have the surgery right away, ending his season, or let him play it out and have the surgery in the offseason, meaning he might not be ready to start spring training.
The team doctors can give you advice all along the way, and the quality of their advice should be based on the team's medical budget. Rest assured your $20 million budget means when your doctor says sit him for 10-12 days, he's probably spot on, but a budget of $6 million means the quack you hired could cause you to bring the guy back too soon, or leave him on the DL for longer than you should have.