The biggest absence, though, may have been Pro-Bowl left tackle Tyron Smith.
Atlanta defensive end Adrian Clayborn had six sacks, setting a team record, and the Falcons dropped Dax Prescott eight times overall in a 27-7 victory that snapped the Cowboys' three-game winning streak.
Chaz Green, who lost his starting spot at left guard after three games, tried to replace Smith and failed miserably.
The Falcons had only 18 sacks coming into the game and just two belonged to Clayborn, a seven-year veteran who had 22.5 sacks for his career.
"I never imagined six sacks," Clayborn said.
Clayborn is just the fourth player since sacks became an official NFL stat with six sacks in a game. The league record is held by Kansas City linebacker Derrick Thomas, who had seven against Seattle on Nov. 11, 1990.
Two of Clayborn's sacks resulted in fumbles by Prescott and he recovered one of them.
"When you get a chance to hit the quarterback, that's where some turnovers are likely to come," Falcons head coach Dan Quinn said.
Clayborn tore a biceps in the playoffs last season, missing out on the Falcons' Super Bowl trip.
"Just think a year ago he was in a dark place, had an injury, and the future was in doubt," Quinn said. "For him to recognize that type of hard work gets rewarded, I was very, very happy for him."
Green was in a dark place Sunday.
"It's unfortunate. You have some good days and you have some bad days. This obviously wasn't my best day," Green said. "I take this on my shoulders. I'm going to look at myself in the mirror and fix the things that I need to fix.
"I just need to stick to my technique. A lot of it was self-inflicted. There's only up to go from here, but this really hurts because I feel like this is on my shoulders."
The Cowboys couldn't contain the Falcons' pass rush without Smith and the defense took a major hit when Lee was lost in the first quarter.
The Cowboys allowed an average of 15 points and 299 yards during their three-game winning streak that followed the return of Lee after he missed two games because of a hamstring strain.
Dallas, which lost safety Jeff Heath with a concussion in the second half, gave up 336 yards to the Falcons, who scored touchdowns on three of four trips to the red zone.
"I think we just fell apart in the second half," Cowboys linebacker Anthony Hitchens said. "Any time you lose it hurts."