SANTA CLARA, Calif. (AP) - Patrick Willis believes the San Francisco 49ers can still be a great defense even without All-Pro tackle Justin Smith.

The 49ers might have to spend the rest of this season finding out whether or not Willis, their All-Pro linebacker and defensive leader, is correct.

Smith is unlikely to play Sunday in the regular-season finale against Arizona because of a partially torn left triceps. The injury could force Smith to miss some or all of the postseason.

The San Francisco defense has been gouged for big yardage and points since Smith was injured early in the third quarter Dec. 16 at New England. But the NFL's second-ranked defense hopes to regroup and regain momentum for the playoffs against an Arizona team that ranks last in the league in total offense.