ENGLEWOOD--Barring an unexpected setback to his left shoulder, Trevor Siemian will be the Denver Broncos’ starting quarterback Thursday night at San Diego, multiple sources told 9News.

Siemian missed the Broncos’ game Sunday against the Atlanta Falcons because of a sprained AC joint in his non-throwing shoulder. His replacement, rookie Paxton Lynch, struggled as the Broncos fell behind the Falcons, 20-3 midway through the third quarter, although he finished strong in what was eventually a 23-16 loss.

The process of having Siemian start against the Chargers actually started when he was informed Saturday he wouldn’t be dressing against the Falcons. Broncos coach Gary Kubiak told Siemian not only that he wouldn’t play against Atlanta, but that he needs to start watching film for the following game against AFC West Division foe San Diego.

“I checked them out Saturday night when I found out that I wasn’t playing,’’ Siemian said. “‘Kubes’ wanted me to do that, so I got a little head start.’’

To test his shoulder physically for the Chargers, Siemian was the only Broncos’ player who wore shoulder pads beneath his jersey during practice Tuesday. The left shoulder injury had been inhibiting Siemian’s range of motion as he passed during practice late last week, and to a lesser extent Monday.

The Broncos listed Siemian as “limited” on their injury report both Monday and Tuesday and he will likely be classified as “questionable” on Wednesday. But he has been getting almost all of the first-team reps this week and providing the shoulder doesn’t experience unmanageable pain in the next 48 hours -- doubtful since the Broncos have nothing more than a walkthrough and meetings in that period -- the Broncos will start him against the Chargers.

“I think I’m expecting to play,” Siemian said.

To help reinforce Siemian's return, the Broncos are also planning to start right tackle Donald Stephenson and tight end Virgil Green, who missed the last three games with calf injuries.