What has been known for a while became official Thursday morning. Cowboys right tackle Doug Free has been placed on the team's reserve/retired list.

Free's retirement opens up $5 million in cap room for the Cowboys this season.

Free, a fourth-round pick by Dallas in 2007, started every game five of the last six seasons. He started 114 games over his 10-year career.

As the team's starting right tackle the last three years, Free was part of a group that had become known as arguably the best in the league.

"Doug was special," tight end Jason Witten said Monday. "Doug was just so solid and he was the rock of that group, amazing leader. He brought his lunch pail to work every day. It's hard to replace guys like that, that they're everything you want in a teammate and in a player and the toughness, but not only the physical toughness, but the mental toughness that they approach it with."

Chaz Green, a third-round pick in 2015, is the front-runner to replace Free in the starting lineup. The Cowboys also added depth at the position by signing veteran free agent Byron Bell last month.

If neither work out, the Cowboys could move La'el Collins to right tackle. But their preference is to keep him as their starting left guard.