SANTA CLARA – Two of the 49ers' defensive starters sat out Thursday's practice, including defensive captain Patrick Willis, who missed the session with a sore knee.

The injury is not believed to be serious. Willis was seen jogging at the start of practice, and he lined up at his usual inside linebacker spot when the defense was participating in walk-throughs.

Cornerback Tarell Brown, who has started all 17 games for the 49ers, also missed Thursday's practice with a thigh injury. Both Brown and Willis were full participants Wednesday, according to the team's participation report.

The good news for the 49ers' defense was that safety Dashon Goldson (ankle) returned on a limited basis after sitting out Wednesday's session.

As was the case Wednesday, neither center Jonathan Goodwin (calf) nor wide receiver Ted Ginn (knee) practiced. While his teammates have been on the practice field this week, Ginn has been getting treatment on his knee, which he injured late in the second quarter Saturday.

If Ginn can't play, Kyle Williams likely would take over Ginn's receiver and punt-return duties, while Kendall Hunter would be an option to handle kick returns.

Walker speaks – Delanie Walker has been outfitted with a face shield and a helmet that is a bit wider and has a bigger face mask than the one he normally wears.

Walker, who broke his jaw in two places Dec. 24, has practiced on a limited basis this week. Walker said Thursday the left side of his jaw has healed to the point where it is just as strong as the right side.

"There's a low chance of me rebreaking it in the same place," he said.

"But it's possible it can happen. This is football. And they warned me of that. But I feel confident in myself, and the doctors feel confident in me to let me go out there with a helmet and do a little bit. So I'm confident I can do what I can."

On Wednesday, Walker started practice wearing a black jersey that designated him as someone who is to avoid contact. Ten minutes into the session, however, the tight end took off the jersey. He wasn't wearing it Thursday, either.

"I felt like I didn't need it, so I took it off," Walker said. "I didn't want to be labeled as not being touched. For me to really know if I can play, I've got to be able to do some contact."

Walker said he still hasn't fully regained the weight he lost when his jaw was wired shut but that he was close and that he was able to stay in shape during his recovery.

Whether he plays or not, he said, will be up to his coaches and team doctors.

York backs Smith – Team president Jed York echoed coach Jim Harbaugh in saying that he wants Alex Smith to return to the 49ers next season. Smith signed a one-year deal before training camp and is scheduled to become a free agent March 12.

"I'm very glad Alex Smith is our quarterback," York said on a national conference call. "I hope he wants to stay here. We'd love to have him here a long time."

The 49ers drafted Smith No. 1 overall in 2005. And while Smith has had a difficult time under San Francisco's previous head coaches, Mike Nolan and Mike Singletary, he always has had a strong relationship with the York family.

"He's battled a lot in his career here," York said. "And I think it's very important when you talk about, you know, Aaron Rodgers vs. Alex Smith, this guy vs. that guy … that quarterbacking in this league is so much about nurture. It's about developing a guy."

More security – York was asked about security at Candlestick Park after reports of boorish behavior toward Saints fans last Saturday turned into a national story.

York said that there wasn't a spike in incidents at the game but that there will be more undercover police officers watching for bad behavior Sunday.

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