The San Francisco 49ers believe Elijah Mitchell suffered a sprained medial collateral ligament in his left knee on Sunday afternoon.

Mitchell returned from a sprained MCL in his right knee just two weeks ago.

The running back is scheduled for further testing on Monday. Mitchell was originally designated as questionable to return, but the Niners ruled him out near the end of the quarter.

Geno Smith has been one of the biggest stories in the NFL this season, but the veteran quarterback isn't shocked by his performance.

He's led the Seattle Seahawks to a 5-3 start in their first season since trading Russell Wilson.

"You've got to be on it every single day," Smith said of the focus it takes to play in the NFL. "A lot of people wish they were in this position and I'm grateful to have worked myself into this position. Also, knowing who I am. I'm very set in who I am and know exactly what I can do. So I never bought into the narrative that's been out there.

"I didn't just get this good over the course of one offseason. I think that's mostly narrative and a lot of that stuff is media driven, but when it comes down to me, people where I'm from know who I am. West Virginia, I just got inducted into the [school's] hall of fame, so people in college football know who I am. The New York Jets as well, the Giants, the Chargers and Seattle. So people have continued to let me know that if I just keep working hard that things will happen for you, and that's what I did."

Smith, 32, wasn't even the clear favorite to start for the Seahawks this offseason after the team acquired Drew Lock as part of the Wilson trade with the Denver Broncos.