49ers’ rookie LB Reuben Foster out with high ankle sprain

SANTA CLARA - Linebacker Reuben Foster left Sunday’s game with what turned out to be a high-ankle sprain, Kyle Shanahan said Monday.

In the locker room after the game, the 49ers’ first-round pick said he’d be back for Sunday’s contest against the Seattle Seahawks. High-ankle sprains, however, usually knock a player out of action for at least two weeks. The 49ers travel to Seattle to play the Seahawks on Sunday, then they host the Los Angeles Rams for a Thursday night game.

Shanahan said he did not have a timetable for Foster’s return.

“We’re putting Reuben in (an orthopedic) boot for a little bit, but those tend to be a month or a little more,” Shanahan said. “I can’t put a date on it.”

Dr. Eric Giza, a UC Davis foot and ankle specialist who is the team doctor for the Sacramento Republic soccer team, said three sets of ligaments keep the lower leg bones intact. A high ankle sprain occurs when one of those sets tear.

“Usually with football players, they’re cutting and then they get hit and their foot sticks,” Giza said. “So their body twists around their ankle and it pops the high ligaments.”

That’s what appeared to happen with Foster as he planted to tackle Carolina Panthers running back Christian McCaffrey in the first quarter while offensive lineman Matt Kalil blocked him.

Giza said there are three grades of severity depending on how many sets of ligaments are affected. A Grade 1 sprain means that just one was ligament damaged. A Grade 3 sprain involves all three sets, can require surgery and would put a player out of action for up to 12 weeks.

That Foster was walking without a pronounced limp in the locker room after the game and downplaying the pain suggests his injury is on the milder end of the spectrum. The medium time frame for NFL players to return to action from the injury is 15.4 days, Giza said.

“In all likelihood it’s a Grade 1 (sprain), the one that’s back in two to three weeks,” Giza said. “Either that or he’s a super tough guy.”

DeForest Buckner, who dealt with low ankle injuries last season and during training camp, said he advised Foster not to rush his return.

“I told him, when he was on the bench, to take it a day at a time,” Buckner said. “The competitive nature in all of us makes us want to get back out there and play. I told him it’s a long season, so he’s just got to get that thing right.”

Foster was leading the 49ers with three tackles and a pass break-up when the incident occurred. On the next play, Panthers quarterback Cam Newton connected with receiver Russell Shepard on a 40-yard touchdown pass.

“He was playing well. He was around the ball a ton,” Shanahan said of Foster. “He got close to a pick, was near another one. He made a good play on a screen right before he got hurt.”

Foster was carted to the locker room where, among other things, team doctors examined him for a broken tibia. He later emerged from the Levi’s Stadium tunnel to cheers from the crowd and stood on the sideline the rest of the game.

His replacement, Ray-Ray Armstrong, tied for second on the team with six tackles. But he also had three mis-tackles, including on a catch-and-run touchdown by Jonathan Stewart.

NOTES

Shanahan said guard Laken Tomlinson, whom the 49ers acquired in a trade on Aug. 31, would compete over the next three practices to start at one of the guard spots. The most vulnerable starter may be left guard Zane Beadles, who gave up a sack Sunday and was the NFL guard who earned Pro Football Focus’ lowest grade on Sunday.

Asked about the 49ers’ three failed fourth-down conversions, Shanahan said the only one he regretted was a fourth-and-4 try in the second quarter. Brian Hoyer ended up being sacked for an 8-yard loss and the Panthers needed only a short drive for a field goal that made the score 10-0.

Aside from Foster, there were no serious injuries in the game, Shanahan said. Fullback Kyle Juszczyk and linebacker Eli Harold both left the game but returned later.