If there was any doubt that the Niners' biggest need next season is for a big upgrade at receiver, it was emphatically eliminated after the vanishing act turned in by the team's wideouts in the divisional-playoff loss to the Giants (only one catch for three yards by Michael Crabtree). The only wide receivers under contract entering the offseason who finished the season on the roster are Crabtree, a major postseason disappointment who had problems holding on to the ball, and Kyle Williams, whose costly fumbles on a pair of punt returns shattered the Niners' Super Bowl hopes. Team insiders hardly would be surprised if the Niners made a major effort in the draft or free agency to land a legitimate No. 1 receiver and then dropped Crabtree into the No. 2 role. As for Williams, word is his playoff blunders have not definitely sealed his fate in San Francisco, contrary to popular belief. "But he will be challenged to make the final roster," one team source said.