McNair, 34, who was placed on injured reserve yesterday, will have his left (nonthrowing) shoulder repaired at a Baltimore hospital. Kyle Boller, who started his third straight game last night, is expected to remain the starter for the rest of the season.
This is the earliest McNair's season has ended - despite his history of injuries, he surprisingly had never been placed on injured reserve - but it's unknown whether his time with the Ravens is over.
McNair, who is signed through 2010, is scheduled to make $4 million next season. The Ravens could create much-needed salary cap room by releasing him.
Asked last month whether McNair would play for the Ravens again, coach Brian Billick said: "That's a question that I really can't answer. Only time will tell that. My admiration for Steve McNair - the champion he's been, the grit, the toughness, the professionalism - is something that I will continue to value. I don't know that anybody can answer that question right now."
Without McNair, the Ravens are left with Boller and rookie fifth-round pick Troy Smith, last season's Heisman Trophy winner.
The Ravens, who promoted kickoff specialist Rhys Lloyd from the practice squad to take McNair's roster spot, likely will sign a free agent to be the team's No. 3 quarterback.
The long-term question is the future of McNair.
Four years removed from sharing the NFL's Most Valuable Player award, McNair slumped in an injury- and turmoil-filled season.
McNair finished this season with more injuries (groin, back and shoulder) than touchdown passes (a career-low two).
In going 2-4 as a starter this season, he completed 133 of 205 passes for 1,113 yards and committed 11 turnovers (four interceptions, seven fumbles). He had a 73.9 quarterback rating, which is 26th in the NFL and ranks as his second lowest since 1998.
McNair began the season by suffering an injured groin early in the opener and experienced back problems a few weeks later.
Then, during the Ravens' 21-7 loss to the Cincinnati Bengals on Nov. 11, McNair partially dislocated his left shoulder and damaged his rotator cuff. He fumbled twice and threw an interception in that game, which was indicative of a mistake-filled season.
One of the NFL's most-injured stars, McNair has never had to have his rotator cuff repaired. Since becoming a starter in 1997, McNair has had at least six surgeries involving (in order) his right knee, lower back, left big toe, right shoulder, left ankle and sternum.
WHAT IS IT? The rotator cuff comprises four muscles and their tendons that connect the upper arm bone (humerus) to the shoulder blade (scapula).
HOW DOES IT TEAR? The wear and tear of aging is the most common cause of rotator cuff tears -- damage that can be exacerbated in athletes -- but a fall, sudden strain or blow to the shoulder at any age can cause a tear.
HOW IS IT TREATED? Doctors typically try a combination of physical therapy, anti-inflammatory drugs and cortisone injections. If they don't work, surgery might be necessary. Full recovery might take as long as six months.
Sources: eOrthopod.com; Dr. Jonathan Cluett, Your Guide to Orthopedics.