The high-priced offensive lineman had right shoulder surgery Tuesday and was placed on the injured-reserve list for the third time in four seasons since joining the 49ers.

General manager Scot McCloughan estimated that Jennings' recovery time would be about six months. The 49ers replaced the eight-year veteran on the 53-man roster by signing tackle Jacob Bender (6-6, 315) off the New England Patriots' practice squad.

Jennings signed a seven-year, $36 million contract in 2005 but he has delivered mostly aches and pains. He has missed 35 of 58 possible starts because of injuries and hasn't played this season since suffering a right-shoulder dislocation against Seattle in Week 2.

Jennings has two years remaining on his deal, including a scheduled salary of $4.2 million for 2009. McCloughan declined to speculate on Jennings' future in San Francisco, saying the matter would be evaluated after this season.

In the meantime, McCloughan sounded sympathetic.

"It's not his fault that he got hurt. It's not his fault that the record is the way it is," he said. "I think he's done everything in his power to try and get back and try to be able to play for us. When he did play for us he has played well. And we've had success with him as a tackle, and they're hard to find."

Jennings held off on surgery this season in hopes of staying on the roster as an emergency tackle. But the emergence of Adam Snyder as the starter and the anticipated return of Barry Sims as a backup meant there was no reason for Jennings to wait any longer.

"It was inevitable," McCloughan said.

Tim McAdams, the team's orthopedic surgeon, performed the procedure in Palo Alto. The goal was to get Jennings' shoulder securely back in place. He suffered previous dislocations in 2005 and 2006.

"It's not a terminal thing. It doesn't mean you can't play again," McCloughan said. "Once you get it buckled down and tight, you can play with it and it's fine."

The 49ers signed Jennings in '05, hailing him as the stalwart tackle who would protect the blindside of quarterback Alex Smith, who had just been taken with the No. 1 pick in the draft.

But Jennings went on injured reserve on Nov. 9 of his first season with a shoulder injury. He played 13 games in '06, but was inactive for three other games with ankle, wrist and shoulder injuries.

A year ago, he started five games before being placed on injured reserve Nov. 5 because of an ankle injury.

"Everybody's built different and some guys are more injury-prone than others, but there's no reason why he can't come back from this once rehab's over and play again," McCloughan said. "There's no reason, whatsoever."