SANTA CLARA, Calif. — The San Francisco 49ers put quarterback Alex Smith on injured reserve Wednesday with a broken bone in his right shoulder, probably ending the former No. 1 draft pick's disappointing four-year career with the club.

Smith, the top pick in the 2005 draft, had surgery on his shoulder in December to repair three torn ligaments, the product of a separated shoulder from a game in late September 2007. He appeared to be at full strength in training camp, but experienced severe pain in his shoulder last Friday while making a long throw during practice.

Dr. James Andrews, who performed Smith's last surgery, confirmed the team's diagnosis of a broken bone in Smith's shoulder, though the quarterback and the team still don't know how it happened. Smith already was struggling with new offensive coordinator Mike Martz's system, losing his starting job to journeyman J.T. O'Sullivan during the preseason.

Smith likely will require more surgery, coach Mike Nolan said. The 49ers signed quarterback Jamie Martin, a veteran of Martz's system, to back up O'Sullivan and Shaun Hill.

The 49ers almost certainly will release Smith before next season, because general manager Scot McCloughan said last week the club can't risk paying $9 million in base salary to a backup quarterback in 2009.

Smith passed for 4,679 yards with 31 interceptions and 19 touchdowns in his first three seasons with the 49ers, who selected the former Utah star with the first draft pick of Nolan's regime. Smith has never found a consistent NFL groove while playing for four offensive coordinators in four seasons and throwing to one of the league's worst collections of receivers.

San Francisco's offense finished last in the NFL in 2005 and 2007. Smith received a share of the blame even though he played only part of his rookie season and missed most of 10 games last year. In 2006, his only full season as a starter, Smith posted respectable numbers for offensive coordinator Norv Turner while the 49ers went 7-9.

Turner then left to become San Diego's head coach.