Dallas Cowboys left tackle Tyron Smith is out for a second straight game because of back and groin injuries for a Sunday night NFC East matchup against the NFL-leading Philadelphia Eagles.
Replacements for the four-time Pro Bowler gave up six of Atlanta's eight sacks in the Falcons' 27-7 win last week.
Byron Bell will start over Chaz Green, who replaced Smith against Atlanta and gave up five sacks to Adrian Clayborn. After Green was benched, Bell allowed Clayborn's franchise-record sixth sack.
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The Eagles, with seven straight wins, have a three-game lead on the defending NFC East champion Cowboys and can all but clinch the title with a win.
Sean Lee had already been declared out for Dallas with a hamstring injury sustained against Atlanta. The Cowboys are 0-2 this season without the 2016 All-Pro linebacker, who missed the earlier games with a hamstring injury as well.
Eagles cornerback Ronald Darby is active after missing eight games because of a dislocated ankle sustained in the opener.