1) Call the person at home or walk up to that person if the person comes back. Ask the person for the reasons. Maybe the person is ill without you knowing it?Search for a possibility to talk two-on-two. Start like: "I'm worried about you, XY. I've seen it in the records that you have been missing, lately, so please tell me now why you have been missing. [Pause for a few seconds, then add:] If something is wrong, is there any way to help you with it? Anyway, please don't hesitate telling me, if you need any help." (This scenario will either make the person feel guilty if the person has been off work for no real reason, and will also give an opportunity for the absent person to open up about problems.)
2) Call or walk up to the person if the person should return: Ask the person not to miss anymore without a signed note from the doctor's, especially, if you are suspicious that the person is just being lazy. Have a two-on-two talk or send a letter, explain why you cannot accept this behaviour, and give out a written warning, if you think your co-worker is just being lazy.
3) After the warning, I would consider firing the person, if it is laziness again.
