Running back Ronnie Hillman isn't on the Broncos' bubble. If healthy, he'll make the 53-man roster, and despite his current listed position of third on the depth chart, is likely to be the primary backup option to 30-year-old starter Willis McGahee.

But the Broncos have yet to get a decent look at the third-round pick in game-time action.

That should change Sunday against the San Francisco 49ers, as Hillman is expected to make his debut after being limited to warm-up drills during the first two preseason games. The injury has provided a valuable lesson for Hillman, who had never endured anything like it before.

"All you have to learn about it is you have to be more careful how you stretch and stay hydrated -- all those different things that go into the hamstring," he said.

Sunday's game is also expected to mark the 2012 preseason debut for safety Quinton Carter, who returned to work this week after missing three weeks following knee surgery.

Carter took part in the team period of practice beginning early last week and said he felt no pain or discomfort, but he lost his first-team slot during his convalescence.

Defensive tackle Kevin Vickerson is also expected to return to the field. He missed a week with a concussion but was cleared on Friday to practice and play, and resumed his work rotating in with the first and second units.

Right guard Chris Kuper (fractured forearm), defensive end Jason Hunter (torn triceps muscle) and linebacker Keith Brooking (hamstring) will definitely not play against the 49ers.

The Broncos did not officially rule out safety Jim Leonhard or second-year linebacker Mike Mohamed, but it would be a surprise if either plays. Mohamed didn't practice all week because of a hamstring injury, and Leonhard didn't take part in team drills until Friday. Broncos coach John Fox said after Friday's practice that he planned to bring Leonhard along slowly. Friday's work was Leonhard's first in pads since he tore his patella tendon last December.

For up-to-the-minute Broncos updates, follow Andrew Mason on Twitter at @CBSSportsNFLDEN and @MaxBroncos.