The injury occurred in the second quarter following a helmet-to-helmet hit by St. Louis linebacker Jo-Lonn Dunbar. The San Francisco 49ers' official Twitter feed confirmed that Smith will not play for the remainder of the afternoon.
Alex Smith is out for the remainder of the game with a concussion.— San Francisco 49ers (@49ers) November 11, 2012
Smith was 7/8 for 72 yards and a touchdown at the time of the injury. He was replaced by second-year player Colin Kaepernick, who is 1/4 for three yards with an additional 14 rushing yards in his absence.
On the season, Smith has thrown for 1,659 yards, 12 touchdowns and five interceptions. The 49ers entered the day with a 6-2 record but trail the St. Louis Rams 14-7 after the first half of play.