He becomes the first player since the regular season began to go on IR.
Also Tuesday, the Niners (3-1) promoted rookie safety Colin Jones from the practice squad to the active roster to fill Tukuafu's spot. Wide receiver John Matthews joined the practice squad. He has experience playing for coach Jim Harbaugh at San Diego.
Tukuafu played in all four games this year, recording two tackles and recovering a fumble. That play came in a 33-17 season-opening win over the Seahawks. Tarvaris Jackson was sacked by Parys Haralson, who forced a fumble that was recovered in the air by Tukuafu on his first career play from scrimmage.