Dallas defensive end DeMarcus Lawrence has been ruled out against Tampa Bay on Sunday night with a back issue that limited him to a season-low 13 snaps last week.
Lawrence, suspended the first four games for violating the NFL's substance-abuse policy, missed practice all week. He was almost held out of last week's 10-7 loss to the New York Giants after his back flared up during the week.
The 24-year-old Lawrence has one sack in nine games after leading the Cowboys with eight last season, his second with Dallas.
The Cowboys lead the NFC with an 11-2 record.
Cornerback Morris Claiborne will miss his seventh straight game with a groin injury. He has said he hopes to return before the end of the regular season.
Backup tackle Chaz Green is out for the 10th straight game with a back injury.