The oft-injured Jennings is healthy, but Nolan wouldn't disclose the reason for the seventh-year pro's absence, which could extend through the 49ers' bye next week — though Nolan said Jennings will return to the team this season.

"As always, our most important interest is in the well-being of our players," Nolan said.

Jennings was at the 49ers' training complex Thursday, but didn't practice. After the morning walkthrough, Jennings consulted with Nolan and team chaplain Earl Smith outside the team's locker room.

Third-year backup Adam Snyder will start in place of Jennings, who started 13 games last season. Jennings won't go back to his offseason home in Atlanta, Nolan said.

Jennings played just three games in his first campaign with San Francisco in 2005, missing most of the year with a shoulder injury. His absence is another blow to the 49ers' already struggling offense, which is last in the NFL in total yards.

Quarterback Alex Smith will miss Sunday's game against Baltimore with a shoulder injury, while tight end Vernon Davis will be out at least one more game with a knee injury.