My player just returned from an injury but he did not receive a "Time of Return" event on his player profile

If your player is close enough to his regularly scheduled development cycle you won't see the effects of his recovery until that time. We do this to save on resources and to improve simulator run speed. If your player has lost ratings there are several reasons why this may have happened (age, length and severity of the injury, your medical staff, and the player's makeup rating to name a few). Please keep in mind that not every player will regain all of his ratings after coming off the DL and it is possible for him to actually lose rating points because of the injury.