They can't fire you for being on medical leave if you set it up with the manager. It could just be some pay checks that you didn't pick up. You would have to open it and find out.
Maybe it's your check stub?
If you're on medical leave, they can't fire you. the fact that it's from payroll and not HR lead me to believe that it's a check.
is the medical leave paid? the package is from payroll so it looks like it's your check or your check stub if you have direct deposit.
Oh, God. Open it! Maybe it is something regarding short term disability.