The Cowboys placed Smith (thumb) on injured reserve Wednesday.
Smith is scheduled to miss four to six weeks to recover from a procedure on his injured thumb. He'll be required to miss at least the Cowboys' next four games, so the earliest that the fifth-year offensive lineman can play is Week 5 against the Buccaneers on Thursday, Oct. 8. T.J. Bass will serve as the Cowboys' starting left guard for as long as Smith is sidelined.