Portrait » The injury news could have been worse regarding Matt Breida

San Francisco 49ers Hats , but it appears the San Francisco 49ers will be without their top running back for at least one game.Breida underwent an MRI on Monday that showed a "serious sprain" to his left ankle, according to coach Kyle Shanahan. That likely will sideline Breida for next Monday night's game at Green Bay."It was positive news that it wasn't a high ankle sprain, (but) he'll probably end up being doubtful this week," Shanahan said.As the 49ers look to rebound from Sunday's deflating 28-18 home loss to the Arizona Cardinals, they'll probably have to do so without the player who's been their best offensive weapon, so far.Breida ranks fifth in the NFL with 369 rushing yards, and his 7.5 yards per carry average leads the league among those with at least 25 rushing attempts. He enjoyed a terrific first quarter Sunday before leaving with his ankle injury.Breida has been a bright spot for the struggling 49ers (1-4) San Francisco 49ers Hoodie , who lost projected starting running back Jerick McKinnon to a torn ACL in the preseason and then watched No. 1 quarterback Jimmy Garoppolo suffer the same season-ending injury in Week 3 against Kansas City.Without Breida, the 49ers would lean heavily on veteran Alfred Morris, who has shared ball-carrying duties with Breida and is more of a between-the-tackles runner.Raheem Mostert is third on the depth chart, but he's more of a special-teams contributor and he fumbled his first carry Sunday after Breida left the game.It wasn't a surprise that the 49ers brought in several running backs for workouts Monday afternoon. One of them was Jeremy McNichols, who was among San Francisco's training camp cuts this summer.Shanahan said the team would decide later in the week whether to sign a running back. Another option is promoting Jeff Wilson from the practice squad if Breida can't play Monday at Green Bay.The 49ers will take a two-day break before returning to the practice field Thursday to begin preparing for their prime-time game against the Packers.Figure a point of emphasis will be protecting the ball better, after San Francisco committed five turnovers in Sunday's loss to the previously winless Cardinals. It was the most turnovers for the 49ers since they had five against Seattle on Sept. 15, 2013.But another challenge for Shanahan is keeping his players mentally focused. Many viewed the 49ers as a potential playoff team before the season. Instead Customized San Francisco 49ers Jerseys , they've lost four of their first five games and suffered a psychological blow when Garoppolo went down."It's different in this day and age where you hear everything," Shanahan said. "It's hard to simplify your world. And with social media, when guys go home, even if guys don't listen to things, their wives do. Their girlfriends do. Their brothers do."When you go through that stuff and don't meet outside expectations, it starts to affect you. And I just try to constantly preach to our guys to be stronger than that, to try to not pay attention to that www.sanfrancisco49ersteamonline.com , because that's not going to help you solve any problems."NOTES: Receiver/punt returner Dante Pettis (left knee) already has been ruled out for a second consecutive game. Several others will be re-evaluated once the team returns to practice Thursday. They include receiver Marquise Goodwin (quad, hamstring), left tackle Joe Staley (knee), center Weston Richburg (knee), tight end George Kittle (knee) and cornerback Jimmie Ward (hamstring).Live updates from Robert Saleh, Richard Sherman Week 3 press conferences The San Francisco 49ers return to practice on Thursday as they continue preparations for their Week 3 road game against the Kansas City Chiefs. The Chiefs are on fire right now, thanks primarily to Patrick Mahomes and his host of weapons. The game is set to kickoff at 10:00 a.m. PT on FOX. Defensive coordinator Robert Saleh is meeting with the media at 12:40 p.m. San Francisco 49ers T-Shirt , and he will be followed by cornerback Richard Sherman. Sherman has spoken to the media the past couple weeks, but this is the first time it’s been mentioned in the media availability release. He spoke regularly in Seattle during game weeks, so this is not surprising. They will be followed by locker room availability from 12:45 to 1:30 p.m. The team hits the practice field at 1:50 p.m. Practice is open to the media until team drills begin, and we’ll get a practice participation report following the session.The 49ers will stream the press conferences Twitter, Facebook, and the team’s app. The 49ers beat writers will also have updates from the media sessions. I’ve embedded our beat writer Twitter list so you can follow along. We’ll have transcripts later today.A Twitter List by NinersNation