Vallos (6-3, 310 pounds) is a sixth-year player who has seen action in 44 career regular-season games (9 starts) with Seattle (2007-09), Cleveland (2010-11), Philadelphia (2012) and Jacksonville (2012), according to the team's press release.
Vallos was a seventh round draft pick of the Seattle Seahawks in 2007 and spent his rookie season on the club’s practice squad before seeing time in all 32 games (eight starts) for the team from 2008-09.
In college, Vallos earned All-America and All-Atlantic Coast Conference honors as a senior at Wake Forest University.
This isn't the answer at center, but clearly the Broncos did their homework at the position when J.D. Walton underwent subsequent surgery a few months ago. They were ready with a contingency plan hours after Koppen went down - even if that plan only involved adding depth.
And yes, I use the word "healthy" with a tone of desperation.