49ers rookie suffers injury that could have big implications for 2025 on first series against Cardinals

It didn't take long for the final game of a San Francisco 49ers season defined by injury adversity to be marred by yet another injury.

In fact, it only took four plays.

Rookie running back Isaac Guerendo suffered what appeared to be a serious injury on the fourth play of the game against the Arizona Cardinals. 

Guerendo was taken off on a cart and quickly ruled out with knee and ankle injuries.

The fourth-round pick has impressed in his time on the field this year, flashing home-run hitting ability and upside in the receiving game.

He would have been hoping to finish the season on a high and put himself in position to compete to be Christian McCaffrey's primary backup next season.

Elijah Mitchell, who missed the entire season through injury, is an unrestricted free agent this offseason. Jordan Mason, who shone significantly in McCaffrey's absence before seeing his season ended by an ankle injury, is a restricted free agent.

If Guerendo faces a lengthy recovery, that could impact what level of tender the 49ers place on Mason, and it could also influence whether they add further to their backfield in this year's draft.

For Guerendo, though, the injury is a hugely disappointing end to a campaign in which he demonstrated why the Niners traded up in the fourth round to add him to their ranks.