One of San Francisco's big-ticket items on defense is done for the year.
Niners starting inside linebacker Kwon Alexander is out for the remainder of the season after suffering a torn pectoral muscle, NFL Network Insider Ian Rapoport reported, per a source. The team later confirmed the news.
Alexander suffered the injury in Thursday night's win over the Arizona Cardinals. The star linebacker played 35 of 50 snaps against Arizona, but didn't see the field in the fourth quarter.
The 25-year-old linebacker joined San Francisco in the offseason on a four-year, $54 million deal after missing 10 games with the Tampa Bay Buccaneers last season with a torn ACL. In eight games this season, Alexander tallied 34 tackles, one forced fumble, one interception and 0.5 sacks.
"Kwon has been great for us this year on the field and as a leader," Niners coach Kyle Shanahan told reporters Friday. "I mean you guys can feel (his energy). I think everyone watching it can feel it and our team feels it. That's how he is on game day, that's how he is on the practice field. The speed he plays with, he's been a great addition for us. It's going to be a tough loss."
In place of Alexander will likely be Dre Greenlaw, a fifth-round rookie out of Arkansas who on Thursday night notched his first career sack.