Mitchell sustained an MCL sprain in his left knee in their 13-0 win over the New Orleans Saints on Sunday, coach Kyle Shanahan confirmed on Monday. Mitchell will be out for six to eight weeks recovering.
The news comes just weeks after Mitchell returned from a sprained MCL in his right knee. Mitchell went down in their season-opener, and was out until Week 10. Now, Mitchell will likely miss at least the rest of the regular season.
"He's pretty disappointed ... To be right back there, he's down on it," Shanahan said, via The Athletic's David Lombardi.
"He's had really bad luck ... Hopefully we can do our job here so when he comes back, we're still playing."
Mitchell went down on a run early in the third quarter on Sunday, and said after the game that his knee was twisted up on the play — though he didn’t expect it to be as serious as his first knee injury. He had 35 rushing yards on seven carries when he left.
Mitchell, 24, has 224 rushing yards on 40 carries in four games this season, his second with the team.
Starting running back Christian McCaffrey had 11 carries for 32 yards in Sunday’s win, which was the team’s fourth straight. He is dealing with “knee irritation,” Shanahan said Monday, and the 49ers are planning to manage throughout the week. They are set to host the Miami Dolphins on Sunday.
With Mitchell now out, and McCaffery banged up, the team will have to lean on third-string running back Jordan Mason and rookie Tyrion Davis-Price. Davis-Price was inactive against the Saints, and Mason had five carries for 25 yards — which was a career-high for the former Georgia Tech running back.
"I think JP [Mason] came in there and did a really good job there at the end," Shanahan said after the game, via ESPN. "They had every single person up there trying to stop the run, and I think you guys saw how hard-nosed he is and how he ran it and was able to keep us out there on the field and not give it back ... Then Ty, we've been wanting to get Ty up."