FRISCO, Texas (AP) -- Dallas Cowboys left tackle Tyron Smith will miss Sunday's game against the Falcons because of back and groin injuries.
The Cowboys said Saturday that Smith and tight end Geoff Swaim were downgraded from questionable to out and didn't make the trip to Atlanta. Swaim injured a knee in practice Thursday.
A four-time Pro Bowl selection who protects quarterback Dak Prescott's blind side, Smith has been battling back issues since last season, when he missed three games. The 26-year-old injured a groin in last weekend's win over Kansas City.
Chaz Green will make his sixth career start in Smith's place. Green started the first three games this season at left guard before losing the job to Jonathan Cooper.
Swaim has been a seldom-used third tight end behind Jason Witten and James Hanna.
The Cowboys signed defensive tackle Daniel Ross off Kansas City's practice squad, but he didn't make the trip to Atlanta. Defensive tackle Brian Price injured a knee last weekend and is out for the season.