SAN FRANCISCO -- The 49ers will be without Joe Staley for next weekend’s showdown with Seattle, but the outlook could have been much worse for the Pro Bowl left tackle.
According to a source with knowledge of the injury, Staley suffered a sprained MCL in his right knee in the first quarter Sunday. An MRI today will determine the severity of the injury and how many games he is expected to miss.
The injury forced the 49ers to reshuffle their offensive line, sending right guard Alex Boone to left tackle, where he faced Rams defensive end Robert Quinn. A candidate for Defensive Player of the Year, Quinn entered the game with 13 sacks and six forced fumbles.
He was shut out in both categories by Boone, who played left tackle all of his life before being moved to guard last season.
“Like riding a bike,” the 6-foot-8, 315-pound Boone said after the game. “Like going back home.”
Boone said he takes perhaps three or four snaps at tackle during practice each week but that he’s still focused on learning how to play guard. Boone said he didn’t spend any time studying Quinn and instead concentrated on defensive tackle Kendall Langford.
Staley’s injury is similar to the one left guard Mike Iupati, who also made the Pro Bowl last year, suffered two weeks ago in New Orleans. Iupati has missed two games but appears close to returning to the lineup.
Adam Snyder started in Iupati’s place, while second-year player Joe Looney, who made his regular-season debut last week against the Redskins when he was on the field for three kneel-down snaps, filled in for Boone at right guard.
Boone said that when Looney entered the huddle for the first time Sunday, the other linemen told him, “It’s time to be a big boy.”
“Joe Looney did a great job stepping up today – hell of a performance coming off the bench and kicking some (butt),” Boone said. “Can’t be more proud of a guy for that. I know he’s going to be ready for (next) week.”
Not faked out – A year ago at Candlestick Park, the Rams brazenly called two fake punts while pinned in their territory. The 49ers fell for both in a game that ultimately ended in a tie.
This year: No dice.
Trailing by 10 deep in their territory and facing fourth and 8, St. Louis snapped the ball not to punter Johnny Hekker but to the upback, Matt Giordano. He intended to pitch the ball to a runner, but the 49ers’ Anthony Dixon broke through the line so quickly that Giordano had to run with it himself.
Dixon wrestled him to the ground for a 5-yard loss. On the next play, Colin Kaepernick hit Vernon Davis for a 17-yard touchdown to seal San Francisco’s victory.
Dixon said the 49ers’ practices were full of fake-punt scenarios.
“It’s the Rams,” he said. “That’s what they do. We were just on alert.”
Et cetera – Ray McDonald started at left defensive end after missing two games because of a high ankle sprain. McDonald had one of the three sacks of Rams quarterback Kellen Clemens.
• Already missing tight end Garrett Celek (hamstring), the 49ers played most of the first half without Vance McDonald, who sprained his right ankle. McDonald returned in the second half.
• A week after the 49ers and Redskins combined for eight penalties, the 49ers and Rams combined for 20, 13 in the first half.
• Return man LaMichael James had three fair catches and muffed a return – but recovered the ball – on one of two punts he took back. After the game, James said he had been dealing with food poisoning.
Read Matthew Barrows’ blogs at www.sacbee.com/sf49ers and listen for his reports Tuesdays on ESPN Radio 1320.