Alex Smith continues to rehab his separated, non-throwing left shoulder, injured in a loss at Carolina on Oct. 24. The Bee reported that Smith had an impromptu end-of-practice throwing session with receiver Jason Hill on Friday.
David Carr will serve as San Francisco's backup quarterback. Singletary will go without a No. 3 quarterback for the second consecutive game.
Troy Smith rallied the Niners to a 24-16 win over the Broncos in London on Oct. 31 -- and the team certainly wants to see if he can do it again. San Francisco is coming off its bye week.
The Associated Press contributed to this report.