SANTA CLARA — Adam Snyder appears headed for a second consecutive start at left tackle in place of Jonas Jennings, who was again held out of practice Thursday by the 49ers because of an ankle injury.

Jennings hasn't practiced or played since suffering a high ankle sprain Oct.21 against the New York Giants. Snyder also started for him Oct. 7 vs. Baltimore while Jennings dealt with a personal matter.

Coach Mike Nolan said Jennings will be back in the starting lineup as soon as he's healthy but there's no timetable. In the meantime, Nolan said Snyder has done a "decent" job at left tackle, though he allowed one of the team's two sacks in Sunday's 31-10 loss to New Orleans.

Sunday at Atlanta, Snyder will match up against defensive end John Abrahan, who is one of the league's better pass rushers. He leads the Falcons with five sacks and has forced two fumbles.

"He's a great pass rusher who's been doing well for a long time, so it will be a good test for me," Snyder said. "He's quick. He's got linebacker's speed playing defensive end, but I've faced fast guys before."

The team's most versatile lineman, Snyder has seen time at every position except center. And though 12 of his 16 starts have been at left tackle, Nolan said his long-term future could be at one of the guard spots.

"My role right now is to kind of be a swing guy — wherever they need me, that's where I need to be able to step in," Snyder said. "I'm prepared to do that, and when you do get your opportunity, you do your best."

Snyder said that mind-set applied to him and the line as a whole in hopes of achieving a breakthrough for their struggling offense. "We as an offensive line are putting that on our shoulders," Snyder said. "It's our job to get the offense going. We welcome that, and we're excited about the fact that we have nine games to play."

INJURY UPDATES: Cornerback Walt Harris (knee) was held out of practice for second consecutive day. If he's unable to play, either Shawntae Spencer or Donald Strickland would start in his place. Safety Keith Lewis (hamstring) also was held out and could miss his third consecutive game. ... Running back Frank Gore (ankle) and tight end Delanie Walker (shoulder) practiced on a limited basis. Nolan said Gore is expected to play, with relief help from backups Michael Robinson and Maurice Hicks.

LEWIS ON LEAVE: Return man Michael Lewis left the team with Nolan's permission to tend to a family matter.

Lewis is expected to join the team in Atlanta in time for Sunday's game. If for some reason he doesn't make it back in time, Nolan said Arnaz Battle and Nate Clements could share punt-return duties.