49ers' Christian McCaffrey Out 6 Weeks with PCL Injury in Knee; Jordan Mason to IR

San Francisco 49ers star running back Christian McCaffrey suffered a PCL injury and is expected to miss six weeks, head coach Kyle Shanahan told reporters:

The injury is not expected to require surgery, Shanahan said Monday.

Backup Jordan Mason is also set to go on injured reserve with a high-ankle sprain.

McCaffrey went down with a noncontact injury in Sunday night's game against the Buffalo Bills, which was played in snowy conditions. He gave himself up on a run play and appeared to be favoring his right leg. At the time of his exit, he had 53 yards on just seven carries.

The team initially announced that he was questionable to return to the game with a knee injury, but he was ultimately ruled out for the rest of the contest as San Francisco suffered a 35-10 loss to fall to 5-7 this season. Shanahan told reporters after the game, "They're saying it's a PCL," and added that McCaffrey could be facing a season-ending injury.

The injury continues a season of misfortune for McCaffrey, who suffered Achilles tendonitis during training camp and was forced to miss the 49ers' first eight games of the year. He made his season debut in Week 10 following the team's bye week and has produced 202 rushing yards and 146 receiving yards.

McCaffrey isn't the only ailing star for San Francisco, as multiple key players have missed time at various points this season. Star defensive end Nick Bosa (oblique) and All-Pro offensive tackle Trent Williams (ankle) missed the last two games. Star receiver Brandon Aiyuk is out for the year with a torn ACL. Even quarterback Brock Purdy missed the team's Week 12 loss to the Green Bay Packers with a shoulder injury.

All of that has created a disappointing season for the defending NFC champions. The 49ers were expected to be one of the top contenders to make it back to the Super Bowl, but they just can't escape their run of bad luck.

Without McCaffrey and Mason, San Francisco will turn to Isaac Guerendo, who has been a reliable ball-carrier when given the chance this year.