Graham went out with an injury late in the game. According to Jeff Howe from The Boston Herald, Graham's left shoe was off on the sideline and he was getting re-taped.
If the star tight end is forced to miss an extended period of time, Drew Brees will have to go to Watson at the tight end position. But it doesn't appear that will be the case, as Graham came back in shortly after, according to Michael Fabiano.
Heading into this game, Watson hadn't been a very productive player. He had just five receptions for 49 yards and a touchdown, which isn't enough to make him a valuable fantasy tight end.
It doesn't seem likely that Graham will miss any time. Even if he does, you probably shouldn't consider picking up Watson, because there are so many other options that could be more productive.