The 35-year-old McNair guided the Ravens to a 13-3 record in 2006, his first season in Baltimore after 11 years in Tennessee. But he injured his groin during the season opener last season and never regained the form that enabled him to earn a berth in four Pro Bowls.

McNair developed back and shoulder injuries and played in only six games in 2007. He threw only two touchdown passes, was intercepted four times and lost seven fumbles before being placed on injured reserve in December, ending his most frustrating season in the NFL.

McNair began his career in 1995 with the Houston Oilers, who eventually became the Tennessee Titans. He led the team to four playoff appearances, including the Super Bowl after the 1999 season. He was named co-MVP of the league in 2003, sharing the award with Peyton Manning, after throwing for 3,215 yards and 24 touchdowns with only seven interceptions.

McNair fought injuries during the latter part of his career with Tennessee and was dealt to the Ravens in June 2006 for a fourth-round draft pick. He signed a five-year contract.

In his first season with Baltimore, McNair played in all 16 games and finished the season with an invitation to play in his fourth Pro Bowl. He threw for 3,050 yards and 16 touchdowns, but was intercepted twice in the Ravens' 15-6 playoff loss to Indianapolis.

Last year, however, was a disaster. After McNair got off to a horrid start, then-coach Brian Billick held the quarterback out for two straight weeks before the team's bye on Oct. 28, hoping the rest would enable the veteran's ailing body to heal. But McNair was ineffective upon his return: He lost two fumbles and threw an interception in a 38-7 defeat at Pittsburgh, then threw for only 128 yards before being replaced in the fourth quarter of a 21-7 loss to Cincinnati.

It turned out to be the last game of his career.

McNair's retirement leaves the Ravens with two quarterbacks: Kyle Boller and Troy Smith. It also increases the probability that Baltimore will seek a quarterback in the NFL draft later this month.