SANTA CLARA — Mario Manningham limped through the locker room on crutches, holding a towel around his waist while trying to keep his head high and sport a smile.
That's not easy to do for the San Francisco 49ers right now.
Manningham is out of the season with a left knee injury after getting tackled low by Leroy Hill and fumbling in the third quarter of San Francisco's 42-13 loss at Seattle. The injury to Manningham, one of San Francisco's signature additions in the offseason, is yet another blow to an increasingly thinning wide receiver corps.
Kyle Williams already is lost for the season with a left knee injury and tight end Vernon Davis did not participate in Wednesday's practice while he recovers from a concussion. Davis took a huge hit from Seattle's Kam Chancellor and must be cleared by an independent neurologist before he can return.
With so many injuries to key receivers, the 49ers (10-4-1) will rely more than ever on Randy Moss and first-round pick A.J. Jenkins to support top threat Michael Crabtree, starting Sunday against the Arizona Cardinals (5-10) in the regular-season finale. Niners coach Jim Harbaugh also said Ricardo Lockette or Chad Hall will likely be promoted from the practice squad.