ENGLEWOOD, Colo. — Center Tom Nalen, the last link to the Denver Broncos' Super Bowl titles of the late 1990s, was placed on injured reserve today, ending his season and likely spelling the end of his career in Denver.

The 37-year-old Nalen, who is in the final year of his contract, underwent two surgeries on his left knee this summer and missed the team's first three games. The Broncos had left him on the roster hoping for his quick return.

The 15-year veteran, whose 2007 season was cut short by a torn right biceps after five games, missed most of training camp before deciding on another operation.

Also Tuesday, the Broncos signed free agent safety Vernon Fox and waived safety Hamza Abdullah, who lost his starting job this summer when he missed most of training camp with a groin injury.

Nalen, whose five Pro Bowls are the most for a Broncos lineman, has helped Denver to the most rushing yards and the third-fewest sacks in the NFL since 1995.

His slow recovery has made center Casey Wiegmann the Broncos' most important free agent signing.

Wiegmann, in his 13th NFL season, spent the past seven seasons with AFC West rival Kansas City. He has started 114 consecutive games in the regular season, the longest active streak among NFL centers, and is anchoring a retooled offensive line that has protected quarterback Jay Cutler despite having no returning starters from last season.

Nalen ranks second in Broncos history with 188 starts and his 194 games rank third in team history. He entered the league as a seventh-round draft pick out of Boston College in 1994, and he was a member of the Broncos' back-to-back Super Bowl teams in 1997 and '98.

Fox is in his seventh NFL season and spent the past two with Washington, which released him Aug. 25. He played in 30 games with the Redskins and started a career-best six times in 2006.

The Broncos also released wide receiver Travis Wilson from its practice squad.