SAN FRANCISCO -- Pro Bowl left tackle Joe Staley sustained a right knee injury on the 49ers' first offensive possession and will not return to action Sunday against the St. Louis Rams.
Staley was injured on a Frank Gore running play. He remained on the ground for a couple minutes as the 49ers' medical staff gathered around. Staley left the field under his own power.
After the 49ers scored on Phil Dawson's 32-yard field goal in the middle of the first quarter, Staley walked to the locker room. The 49ers announced that Staley would not return to action.
Right guard Alex Boone moved to left tackle, and second-year player Joe Looney took over Boone's spot at right guard. Staley has started every game for the 49ers since the 2011 season.
The 49ers were already playing without one starter on the offensive line, as Adam Snyder began his second game in Mike Iupati's absence. Iupati is out with a knee injury.