Alex Smith insists it's too early to guess whether he will return from a concussion in time to start at quarterback in San Francisco's key Monday night NFC showdown against the Chicago Bears.

The decision is not up to him, anyway.

Smith went through position work with the NFC West-leading 49ers (6-2-1) in a non-contact black jersey Wednesday, his status still unclear after he sustained a concussion in the second quarter Sunday against the St. Louis Rams.

"I feel good, better," Smith said Wednesday in his first comments since the injury. "I'm just going along with the process right now. Nothing's been decided. It's a whole long process that's up to the doctors. I just kind of do what they tell me. Contact obviously is the final straw."

Coach Jim Harbaugh kept a watchful eye on Smith from several yards away as he worked with backup Colin Kaepernick and No. 3 QB Scott Tolzien to get his reps.

Smith had to pass concussion tests given by a neurologist -- he went to Stanford on Monday -- to get this far and return to the practice field, but there are still further steps in the process for him to be medically cleared for game action.

"Right now it looks like Alex will be our quarterback for sure," optimistic tight end Vernon Davis said. "I would think so. With all those concussions, you can't really tell, but he was out there and threw the ball around a little bit."

Smith said he experienced blurred vision on a 1-yard quarterback sneak early in the second quarter of Sunday's 24-24 tie. But six plays earlier, he scrambled to his left and started to slide before turning when St. Louis linebacker Jo-Lonn Dunbar hit him in the back of the neck with 1:10 left in the first quarter. Smith briefly grabbed his face mask and grimaced but stayed in the game.

He isn't sure whether that hit contributed to the concussion, because he didn't experience any symptoms right away.

"It's all speculation. It certainly didn't help," Smith said. "Talking to the neurologist, it probably contributed, for sure. Whether it loosens you up for the next one, I don't know. I felt fine after that though. The sneak was definitely when I came up and my eyesight went wrong."

So, just how did he manage to complete all three passes he threw afterward with blurred vision, including a 14-yard touchdown to Michael Crabtree?

"That's a great question," Smith said. "No idea. It certainly wasn't like I was blind."

But he was hurting.

Smith said he experienced headaches and nausea with the concussion, and the symptoms were "more severe" than what he felt after a concussion last season against Dallas in the team's home opener. By Monday morning after sleeping overnight, Smith said he had improved.

"It's tough to describe. For me, the vision was the biggest thing, for sure," Smith said. "I've taken a lot of hits over the years, and to try to play quarterback when you're vision is not what it should be was difficult," Smith said. "For me, ultimately it didn't get better. It wasn't one of those things I could blink off and my focus was returning. I went on the sidelines and sat down and it seemed to get worse. It wasn't getting better. It was not good for the team to go out there. I didn't think I could help us much."

Second-year backup Colin Kaepernick took over for the second series in the second quarter and rallied the Niners in the fourth quarter, even running for a 7-yard touchdown. He finished 11 for 17 for 117 yards with three sacks.

He is approaching as if he will start against the Bears -- the same way he prepares every week.

"Same reps as always. Nothing really changes," Kaepernick said. "I've always been out there preparing myself to start."

The rest of the 49ers aren't worrying about who will be quarterback, just preparing for the stingy Bears defense.

"Whoever's behind center, we'll be ready to go," left tackle Joe Staley said.