Yes, but ONLY in full-season leagues - there are no injuries in the exhibition season games. Guys can go down for a play and come right back or be out for 1 or more games.
If a player is injured in the game, it will be highlighted in RED in the play by play.
If he can not return to action in the current game, his injury status will be displayed in your coach's office next to his name. In addition to the injury, you'll also see the expected return date. Until he is cleared to return to action, the player will be unavailable to play.
Injuries are based on how many total minutes the player played in real life. You should look at real life total minutes divided by 82 to determine about how many minutes they can play per game in the SimLeague. If you try to play someone more than that number, they may suffer an injury in addition to any fatigue.
If you do not have 5 healthy players at tipoff, you will forfeit that game. At any time during a game, if you can not produce 5 healthy players, you will also forfeit.