UPDATE: Per Mike Klis of the Denver Post, with the Broncos' depleted TE corps (see below), Julius Thomas "has been getting his first-team chances at the 'F' or 'move' or 'receiving' tight end position throughout the offseason and training camp," while Virgil Green "is a prototype 'Y' tight end, who plays at the line of scrimmage."
Basically, that means that Thomas is more likely to end up catching passes if Joel Dreessen and Jacob Tamme end up out during the regular season, but as I noted below, it's kind of a moot point in fantasy terms.
The setback that Joel Dreessen sustained with his surgically repaired knee will force him to undergo another procedure to repair damage in the joint. It's expected to keep him out for the entire preseason, according to ESPN.com's Jeff Legwold.
"The Broncos formally break training camp just before their Aug. 17 preseason game in Seattle, but Dreessen is now expected to be held out of all four preseason games," he wrote. "The surgery, the date of which it will occur was immediately unclear, will be the second surgery Dreessen has had on the knee in just over two months."
Dreessen had been working as the top tight end early on in camp, though the team runs plenty of two-TE sets with Jacob Tamme on the other side. With Dreessen out, and Tamme nursing a sore thigh, Julius Thomas will have a chance to work as the top option and Virgil Green will get more work, too. Thomas carries some intrigue as a former basketball player, who is finally healthy after battling an ankle injury the past two seasons.
None of the Broncos TEs are likely to be reliable fantasy options, though; there are four of them fighting for snaps, and the addition of Wes Welker in the slot surely will diminish the number of passes targeting tight ends this season.