San Francisco 49ers quarterback Alex Smith left Sunday's game against the St. Louis Rams with a concussion.

Smith suffered the concussion late in the first quarter on a quarterback scramble. As he began to slide, he turned his back to linebacker Jo-Lonn Dunbar, who hit Smith around the neck area.

Smith stayed in the game temporarily and even threw a touchdown pass to Michael Crabtree in the second quarter.

Colin Kaepernick replaced Smith later in the frame.