First, they want to make sure the right tackle's injury has fully healed. Jennings, the 49ers' marquee free-agent acquisition in 2005, has suffered two other dislocations to the same shoulder -- in 2005 and 2006 -- and earlier this year he wondered aloud to reporters whether there was an underlying problem.

Asked whether Jennings was healthy enough to return to the starting lineup, coach Mike Singletary on Friday said, "We really won't know until we need him. To me right now, the more he's out, the better. It gives him time to get stronger."

The other reason Jennings hasn't been rushed back is Adam Snyder.

Snyder started the season at left guard but was replaced three weeks ago by David Baas. The demotion, though, was short-lived when Barry Sims, who was Jennings' backup at right tackle, hurt his foot. Snyder filled in well in that game.

On Monday against Arizona, Snyder had perhaps his best game of the season.

"Right now, he has to earn that," Singletary said of the possibility of Jennings regaining his starting job. "I think Snyder is working his tail off. ... Right now, Snyder's the guy."

Last weekend, the 49ers, who with the Detroit Lions lead the league in sacks allowed, did not give up a sack, the first time since December 2006 they have achieved that feat.

Left tackle Joe Staley also noted that Arizona had the league's longest streak for games with a sack -- 31.

"Overall, it was probably our best game," Staley said. "We might not have individually had our personal best games, all five of us, but as a group we played well."

Gore back -- Singletary said Frank Gore "moved well, ran well" in practice and should be fine for Sunday's game. Gore is listed as probable with a neck strain.

Gore was a source of confusion Thursday when he initially said he suffered a concussion late in Monday's game before later agreeing with the team that the injury was to his neck. Gore said he jammed the neck when attempting to block Arizona defensive end Chike Okeafor in the final minute.

He said his body went numb following the collision. He had to be helped to his feet and sat out a play before returning for the final three plays, including a critical short run in which he stumbled in front of the goal line. Gore said Friday he had been receiving ice and massage treatments for his neck.

Safety in numbers -- Starting safety Mark Roman is questionable with a groin injury, although Singletary said he was encouraged with how he practiced Friday.

If Roman cannot play Sunday against the Rams, Keith Lewis (Valley High School) would make his first start of the season. Lewis has been filling in for No. 3 safety Dashon Goldson, who is out with a knee injury.

Read Matthew Barrows' 49ers blog at www.sacbee.com/ninersblog.