Ack! I didn't notice the doctor. That's a good point. DPB said that everyone would have a secret. Maybe Tony's is that he's sick (and this would be different from the spoily "Director Shepard and Tony will share a secret")? Maybe he has developed problems from having the plague? Maybe cancer? Maybe... Argh -- I'll just wait until the episode airs. I'm sure it's nothing -- probably just him visiting his girlfriend.
Plague? Cancer? Is it already time for the annual Someone-is-leaving-NCIS-at-the-end-of-the-season-rumor?
I think he uses the doctor-excuse for his visits at Ms.Benoit. There he is on his own. When he did the undercover job on the airport (errands for the director) there were certainly more persons involved.