While the San Francisco 49ers were naturally disappointed to lose Christian McCaffrey to a PCL injury against the Buffalo Bills, the silver lining behind the latest setback for the reigning Offensive Player of the Year was the opportunity it appeared set to provide Jordan Mason.

Mason, who had led the way on the ground during McCaffrey's absence from Achilles tendinitis, impressed against the Bills to the tune of 78 yards, taking him to 789 for the season.

A long-term absence for McCaffrey, which was confirmed on Monday as he was placed on injured reserve, would have given Mason the chance to reach 1,000 yards, had Mason not himself suffered an injury that looks likely to end his season.

Kyle Shanahan revealed on Monday that Mason will also be placed on injured reserve with a high ankle sprain, robbing him of the chance to join a 49ers Hall of Famer in an exclusive club with a 1,000-yard season.

Of the 11 players to have amassed 1,000 yards rushing in a season for San Francisco, the only undrafted player is the late Joe 'The Jet' Perry, the Hall of Famer doing so twice in his storied career.

Mason will now likely end his season 211 yards shy of joining him. Had he not hurt his ankle, Mason would have been expected to get up to four figures easily over the course of the final five games of the season.

Instead, rookie Isaac Guerendo, who scored the 49ers' only touchdown in the loss to the Bills, now gets the chance to lead the backfield the rest of the way.

The fourth-round pick, who was the fastest running back in the 2024 draft with his 4.3 speed, has already displayed his big-play ability during limited action on offense this season. His 15-yard scamper in Buffalo marked his second NFL touchdown, Guerendo's first having come in the Week 8 win over the Dallas Cowboys in which he rushed for 85 yards.

Guerendo also had a game-sealing 76-yard carry in a Week 6 triumph against the Seattle Seahawks.

Now he has the opportunity to turn those enticing flashes into consistent production as the 49ers look to stay alive in the playoff race. Should he do so, Guerendo could build a strong case for entering next season as the number two back ahead of Mason, who is a restricted free agent next offseason.

The likelihood is that the 49ers will keep Mason around but, instead of having a shot at an impressive piece of history, he must now watch as his teammate tries to construct an argument for moving ahead of him in the pecking order next year. It's a cruel twist of fate for a player who deserved to complete a fine personal achievement.

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