SANTA CLARA, Calif. — Jonas Jennings was well on his way to a fresh start with the 49ers until he heard that familiar pop in his right shoulder on Sunday.

Jennings immediately knew it meant more of the same misery that has defined his star-crossed career in San Francisco.

The high-priced offensive lineman will miss the 28th game of his three-plus seasons with the 49ers on Sunday with a dislocated right shoulder. Jennings has dislocated that shoulder three times in a San Francisco uniform, and the latest injury has left him a bit embarrassed by the struggle to stay healthy.

"It just takes one play, and there it goes," Jennings said. "I've got to find out in my mind if there's underlying problems, and what (they) may be. Coming in, I felt I had probably one of my best offseasons, one of my better camps. That's what makes it embarrassing."

After three disappointing seasons with Jennings as their starting left tackle, the 49ers moved him to the other side of the line this season in an attempt to remove some of the pressure of being in the line's highest-profile position. Jennings hasn't always handled scrutiny well, and the right tackle spot seemed to agree with his disposition.

Jennings was among the 49ers' most impressive players in training camp, and he looked good right up until that trip to Seattle. He committed two false starts and a holding penalty before leaving the game with his injured shoulder, which was diagnosed later as a dislocation.

Jennings' right arm is in a sling again, and the 49ers don't know how they'll treat the injury. Surgery still is an option, but it might only need rest — and Jennings would love to avoid a third surgery on the shoulder.

"I've got a chance," Jennings said. "I've got to visit with doctors, just kind of roll with the medical staff and do what they ask me to do. It's to the point of frustration for me. I just want to do whatever I can to play football again. Even if it was the surgery option, I probably wouldn't jump to it at this point."

The 49ers clearly like Jennings' abilities or he would have been dropped last season, when he missed 11 games and eventually went on injured reserve with a litany of problems, including a one-game absence for still-unexplained personal reasons. Coach Mike Nolan clearly grew frustrated with his oft-injured tackle, who was his most prominent free-agent signing in early 2005 when he took over every aspect of the 49ers' football operations.

Nolan has remained supportive of Jennings, insisting he didn't blame the tackle for his two false starts in the Seahawks' notoriously noisy stadium.

"He wasn't the only culprit early with the noise and all that was going on," Nolan said. "He just got hurt prematurely, (before) the time he could get it all together, like some others."

The 49ers shouldn't lose much in his absence. Barry Sims, a 10-year NFL veteran who spent his entire career with the Oakland Raiders before signing with San Francisco in late June, stepped in and played fairly well when Jennings got injured.

"I'll start until they tell me I'm not starting any more," said Sims, who chose the 49ers among several free-agent suitors partly because he suspected he'd get a chance to start. "I wasn't rooting for Jonas or (left tackle) Joe (Staley) to get hurt. I don't know if we're better with me in there, but I'm committed to this team, and I'll do everything I can to get the job done."