49ers Rumors: LB Kwon Alexander Out for Season with Torn Pectoral Injury

San Francisco 49ers linebacker Kwon Alexander is out for the season after suffering a torn pectoral during Thursday night's 28-25 victory over the Arizona Cardinals, according to Ian Rapoport of NFL Network.

Though he was unaware of his status moving forward at the time, Alexander remained positive after the game:

NBC Sports Bay Area's Matt Maiocco reported on Thursday that the team had "some level of optimism" regarding the injury. The linebacker underwent an MRI on Friday to determine the full extent of the injury.

Unfortunately for the Niners, they will now have to chase a Super Bowl without the 2017 Pro Bowler.

It's a tough break for Alexander. A fourth-round pick in 2015, he spent the first four years of his career with the Tampa Bay Buccaneers. He was limited to just six games in his final season in Tampa Bay last year due to a torn ACL.

The 25-year-old signed a four-year, $54 million contract with San Francisco in March, receiving $27 million in guaranteed money.

San Francisco's pass defense has played a big role in the team's 8-0 start. The 49ers own the top-ranked pass defense, allowing just 138.1 yards per game. Meanwhile, they are holding opposing passers to a 65.7 rating (second in the NFL) while having recorded 10 interceptions and 30 sacks, both of which are tied for the second-most in the league.

And Alexander had played a role in that success:

Alexander piled up 34 tackles, 0.5 sacks, one forced fumble, one interception and four pass breakups in eight games.

"It's going to be a tough loss," Niners head coach Kyle Shanahan said, per KNBR's Jake Hutchinson.