Part of the reasoning behind the switch back to Troy Smith is based on the fact that he already beat the Rams and Arizona Cardinals -- the remaining teams on the 49ers' schedule -- according to the source.
Troy Smith has shown a better understanding of the playbook and a hunger to play, realizing this might be his last opportunity to make a statement about his ability to be an NFL quarterback. Smith had his best game as a pro during a Nov. 14 victory over St. Louis, completing 17 of 28 passes for 356 yards, one touchdown, no interceptions and a 116.7 rating.
Troy Smith initially filled in after Alex Smith separated his non-throwing, left shoulder during a Oct. 24 game against the Carolina Panthers and then kept the job even after the 2005 No. 1 overall draft pick was healthy again.
"No, we have not finalized that," Johnson said. "We're still trying to figure that out. We are practicing both guys, and that decision will be made later."
Singletary said Tuesday that he already had decided who would start between Alex Smith and Troy Smith, but that "it's something that I don't really want to announce right now."
One day later, Johnson said he had no knowledge of Singletary's decision.
"I've been told that he wants me to practice both quarterbacks and give both quarterbacks reps in practice," Johnson said. "I'm going to do exactly what I've been told to do. I'm going to make sure both guys are prepared to play. I've got to find a starting quarterback for the next four quarters. That's the deal. I'm sure (Singletary) will let me know, and we'll decide and go from there."
If the 49ers (5-9) win their final two games, they could finish in a three-way tie with the Rams and Seattle Seahawks and claim the NFC West title -- ending a seven-year playoff drought and making good on team president Jed York's declaration that San Francisco would rebound from an 0-5 start to reach the postseason.
Rookie running back Anthony Dixon, whose role in the 49ers' offense has significantly increased since starter Frank Gore was lost for the season Nov. 29, said the uncertainty at quarterback isn't affecting the team's preparation this week.
"It's not difficult, because you've got to do your job first," Dixon said. "The quarterbacks, they're going to get their job done. I'm just worrying about doing my job right."
The Associated Press contributed to this report.