Jennings was the team's marquee free-agent acquisition early in 2005. The 49ers snagged him to a $36 million contract, and the intent was to have Jennings anchor the offensive line and protect the blind side of quarterback Alex Smith, who would be drafted a month later.

Both players' careers, however, have been stalled by shoulder injuries.

Jennings missed 13 games that season and suffered the first of three right shoulder dislocations. Jennings has had three surgeries on the shoulder, the most recent occurring Tuesday morning. Jennings never made it through a full season in four years with the Buffalo Bills , and he's missed 35 of 58 possible starts since joining the 49ers.

Jennings has two seasons remaining on his contract. If the 49ers cut him, his salary would still count against the salary cap in 2009, but the team would save a little more than $3 million. He would be off the books by 2010.

"We'll address this at the end of the season," general manager Scot McCloughan said in a conference call. "He's got two years left under contract. Durability has been a question. It's something we're going to address at the end of the season. But as of right now he's a 49er. It's not his fault that he got hurt. It's not his fault that the record is the way it is. I think he's done everything in his power to try and get back and try to be able to play for us."

Jennings was unavailable for comment Tuesday, but told reporters after his most recent injury in Week 2 against Seattle that he was annoyed and embarrassed by his spate of injuries and he wondered whether there was an underlying issue that would prevent him from playing again.

"When I go on the field, I can't be thinking about it every play whether my shoulder is going to come out," he said. "I'm going to continue to play the game violently. That's the way I do it. Still, it's something to think about."

Jennings has participated in practice the past two weeks while wearing a shoulder harness. He was the emergency backup at tackle Sunday against St. Louis. But trainers determined that the shoulder wasn't progressing and decided not to put off surgery any longer. The rehabilitation process will take six months, McCloughan said.

The 49ers could afford to place Jennings on IR because Adam Snyder has played well at right tackle during the past 21/2 games. Snyder's addition to the starting lineup has coincided with an overall resurgence of the offensive line, which has allowed two sacks in the last two games.

McCloughan said the team expects tackle Barry Sims to return from a foot injury this week. The 49ers also signed a tackle, Jacob Bender, to fill Jennings' spot on the roster. Bender was a sixth-round draft pick by the New York Jets last year out of Nicholls State. He was on the Patriots' practice squad when the 49ers signed him.

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