It was a gut-check of a win for the San Francisco 49ers when they escaped the clutches of the rival Arizona Cardinals on Thursday Night Football, but they did suffer a major loss in their 28-25 victory. Starting linebacker Kwon Alexander, whom the team signed this year to a four-year, $54 million deal with $27 million guaranteed, will not return to football this season.

The 25-year-old was scheduled to undergo an MRI on Friday and did, with the results reportedly revealing a torn pectoral muscle -- per Ian Rapoport of NFL Network -- that will require surgery to repair and land him on injured reserve. It's a huge blow for a 49ers defense that has been dominant and mostly carried the team throughout their 8-0 start, and marks the second consecutive year Alexander will be unable to complete a season.

For his part, although he didn't confirm the official diagnosis, Alexander has a message for all to hear.

In 2018, as a member of the Tampa Bay Buccaneers, Alexander landed on injured reserve after suffering a torn ACL in Week 7. Now in his fifth season, Alexander has played a full slate just once, back in 2016 when he broke out with 145 combined tackles, three sacks and an interception -- establishing himself as a star at the professional level. 

Hoping to get back on the wagon in a big way in 2019, he played in all eight games thus far and was a key part of what the Niners did on defense. Not having him on the field creates a void they'll need to fill somehow, and quickly, because outside of their matchup with the lowly Atlanta Falcons in Week 15, their second-half schedule is a take-no-prisoners gauntlet. 

For Alexander though, and for the second time, it's about hitting the reset button and trying again next year.