Cowboys starting left guard Tyler Smith will undergo thumb surgery and is headed to injured reserve, head coach Brian Schottenheimer announced Monday. Smith is expected to miss four to six weeks.

Per NFL Trade Rumors, the thumb issue has been bothering Smith for some time before the decision was made to have it surgically repaired. Smith was absent from the team's Monday practice, according to Blogging The Boys.

The injury leaves Dallas without a starting offensive lineman for the first portion of the regular season.