The 49ers without linebacker Patrick Willis

SAN FRANCISCO -- The San Francisco 49ers came into Sunday hoping to claim the NFC West title.

Losing linebacker Patrick Willis to a hamstring injury wasn't part of the plan.

The 49ers said Willis' return to the game was doubtful. Willis stayed down after failing to finish an attempted tackle on the perimeter against Rams fullback Brit Miller.

Willis reached back for his leg while on all fours. Medical staff helped him off the field. At least seven doctors/trainers tended to Willis while the Pro Bowl linebacker sat on the bench. Willis rose and walked slowly up and down the bench area, slapping hands with defensive teammates as if to encourage them.

Larry Grant took over for Willis. It's unclear how long Willis might be out. The 49ers have four additional regular-season games. Securing a first-round playoff bye would give Willis a couple extra weeks to get ready, should he need it.