One of the things that the Saints do well is exploit Reggie Bush's ability to make things happen in space. Drew Brees has thrown Bush the ball forty times already this year and he's turned those passes into big plays, averaging 8.3 yards per catch and leading running backs in receiving DYAR and Effective Yards while racking up 257 yards and two touchdowns on 31 receptions.
The Vikings as a team, however, are normally well situated to shut down those passes. When a team has fast, sure tackling linebackers like Chad Greenway and E.J. Henderson and are able to get pressure without blitzing (which the Vikings kind of do), it's no surprise to see that they have a -6.1% DVOA against running backs in the passing game.
As I said, normally, I wouldn't worry too much about the Vikings' linebackers ability to shut down Reggie Bush, and, quite possibly, the rest of the Saints' offense with him. But that was before E.J. Henderson was unable to practice today due to his dislocated toes. Without Henderson, the Vikings are down to one Pro Bowl caliber linebacker in Greenway. He's been very good this year (remember, he's 5th in the NFL in tackles this year), but he'll be the only one on the field that can match up with Bush, making it that much harder to ensure the Vikings get the match up with Bush that they want. With Henderson on the field, it provided the margin of error that any good defense needs in play calling. Now, it's just that much easier for the Saints to get the match up they want, which means it's that much easier Reggie Bush to break that big play the Vikings need to avoid if they want to win. And at 1-3, the last thing the Vikings want is something making it easier for their opponents to win.