The good news for Saints fans is that Graham's injury doesn't appear to be serious, according to a Pro Football Talk source:
Per a league source, Graham has a sprained shoulder that currently isn't believed to be serious.
Hopefully this source is legitimate.
Graham returned to the game after initially injuring the shoulder but eventually left again and never returned which might be an indication that it wasn't too bad and that the team simply decided to just play it safe. The other good news is that Graham gets an extra week to recover, as the Saints have a bye in Week 6.