Information is sketchy so far, but it appears that Miller could be hit with a four-game suspension for violating league policy. What policy is unclear at the time; no one has stated whether its the PED policy or substance abuse.
While there is no good timing for such a suspension, the beginning of the season will especially hurt the Broncos defense. After losing Elvis Dumervil during the off-season the team is going to need Miller to step it up a notch. With 18.5 sacks last season that sets the bar pretty high for him.
Should he lose the appeal the team will be without him for games against the Ravens, Giants, Raiders, and Eagles. Even with all the free agent losses you know the defending Super Bowl champs will be tough. Tom Coughlin will likely figure out some way to help Eli Manning exploit Denver's weakened defense. Both the Raiders and Eagles are expected to be much tougher this coming season as well.
It's unlikely that they would drop all four with Peyton Manning at the helm of the offense, but part of the reason the team was so successful last year was because the defense was able to take pressure off of him and the offense. That will not be easy with Miller and Dumervil out of the lineup.