Rivers left last week's win over Chicago early with that injury, and did not practice all week. Nigel Bradham returns to the starting lineup from a one-game suspension, but with Rivers down, rookie Preston Brown will likely make a second straight start this week.
Backup tight end Lee Smith was able to return to the practice field this week, but is listed as doubtful as he continues to deal with a toe injury. In the likely event he can't suit up, the Bills will need to make alternate arrangements for aiding rookie right tackle Seantrel Henderson in blocking Miami's fiercest pass rusher, Cameron Wake; having Smith would have been a huge asset on that front.
Jonathan Meeks is also listed as doubtful with the neck injury that has kept him out of the lineup since August 9.
On the positive side of things, four players are listed as probable, including starting defensive backs Stephon Gilmore (groin) and Aaron Williams (head). Gilmore was close to playing in Chicago, so his elevated status is not surprising, but there was some question regarding whether or not Williams would be able to play with his concussion symptoms. It's looking like the Bills will have all of their primary defensive backs healthy and available on Sunday.
Sammy Watkins (ribs) and Chris Hogan (ankle) are both listed as probable, as well. Both players finished the win over Chicago despite their ailments.