Quinn also ruled out kicker Matt Bryant, who will miss a second consecutive game due to a right hamstring injury.
Rookie Isaiah Oliver will start in place of Alford, while Giorgio Tavecchio will handle the kicking duties for Bryant. Tavecchio earned the NFC special teams player of the week honor for his performance in a Week 7 win over the New York Giants, which included a career-long 56-yard field goal.
Quinn did not provide an immediate timetable for Alford, who apparently injured his ankle against Giants but played 98 percent of the snaps. Alford appeared to be unable to run while going to rehab exercises Friday.
Both Quinn and defensive coordinator Marquand Manuel expressed confidence in Oliver, a second-round pick from Colorado. Quinn said he has seen more discipline at the line of scrimmage from Oliver since a late-game mishap in a loss to Cincinnati. Manuel has seen the same.
"He has to be prepared, as a professional, to go in and dominate his role, what we're asking him to do: Stay on top, tackle, get the ball," Manuel said.
Injuries have been a common theme for the Falcons this season, with six starters placed on injured reserve: linebacker Deion Jones, strong safety Keanu Neal, free safety Ricardo Allen, running back Devonta Freeman, left guard Andy Levitre and right guard Brandon Fusco.
The Falcons can designate two players to return from IR, and Jones is inching closer to a return while starting to rehab on the practice field. He is eligible to return to game action for the Nov. 18 matchup with Dallas; Freeman could return for the Dec. 23 game at Carolina.