Last September, Walton broke his ankle in a late September contest against their AFC West rivals, the Oakland Raiders. Walton was lost for the season when he was placed on Injured Reserve shortly after that game. Walton underwent surgery in October, but clearly the issues were not resolved completely.
Walton is an important fixture along the Broncos offensive interior. Protecting Peyton Manning is the primary objective for the Broncos' success, and the line already had questions with Ryan Clady's contract dispute and Chris Kuper's offseason surgery as well. Kuper, one of the team's starting guards, declined an invite to play in the Pro Bowl to go ahead with surgery to repair a fibula break.
Expect the Broncos to check out free agents now that the team has multiple question marks among its starting unit.