You are confusing being in shape with football shape.
Gettis was a track star. I highly highly doubt he would allow himself to get out of shape. He's probably never been out of shape in his life.
If there were some physical problem, Rivera wouldn't have stuck him in for 2 plays and yanked him out again. If a guy is really either injured or out of shape, you don't toy with them and their health. You put players in the game who are healthy, and if they're not, you keep them out.
Putting him in and yanking him out is sending a message.
But the bigger picture is......he is competing for a spot to be our rec 4th target. We don't have lots of plays for that role right now